Anyone with a website knows that mobile usage is the fastest growing statistic on their site. Yet, apparently, according to some observers (and Apple's own financial statements) Apple suffered a 16% drop in iPad sales in its last reported quarter. Are tablet sales slowing down then? No, says Apple, ascribing the figure this to a one-off inventory issue.

What about Tesco's 7-inch Hudl Android tablet? This machine has sold half a million units since it was introduced last September. Maybe tablet sales are up then? And does this mean consumers prefer smaller screen devices to traditional large screen tablets?

It's all too confusing. Maybe smartphone developments reveal more; though it still has a clear lead in overall tablet shipments, Apple is facing lots of competition in smartphones. In the Android space alone, for example, we are now seeing phones sporting 4in, 5in and 6in screens, as well as a new name for these bigger screen devices; 'phablets'.

What's happening with mobile devices? Does it matter?

The mobile sector is not in decline in the way that PCs and now notebooks are, but is simply maturing and diversifying to satisfy a wider range of niche uses. And yes, it does matter. There is a compelling reason keep up with these changes, since any CIO managing an online presence – that's any company therefore – needs to know how their users are access their site and services, so that they can be delivered in optimised format. That now means offering on-screen solutions that are satisfactory whatever the client's screen size.

Many (most?) companies are on the case, already zoning in on perhaps large screen and mobile version of their site. Those that aren't will get there soon enough.  But in a world where phones can have screens as big as tablets and tablets are now appearing with notebook-sized screens, is a two-screen split enough?

Operating system based device apps used to be the way to address these issues, but as the number of devices and operating systems multiplies, the complexity of building a maintaining an array of apps is becoming untenable. Few of even the largest internet companies do a good job with their apps across the board. In any case, improved data connectivity probably makes your web site the best place to drive customers in the future.

Here, it's responsive web design which flies the flag for a single site, capable of delivering many client variations. A responsive site layout is dynamic and client dependant, so that all the necessary page elements can be displayed whatever the screen size – the aim being to become screen agnostic. Giving the current activity of hardware manufacturers, that seems a smart policy for us all to adopt.

There's another pay-off: A single site delivered to all devices is preferred by Google's search algorithm, so will improve the site ranking compared with different mobile and large screen sites. And your content people and site management you will be dealing one website, CMS and its content.

But such agnosticism comes with its own problems, particular where businesses really rely on their web presence for revenue and sales. As any e-commerce site owner will know, tiny changes in layout, design and page structure can have significant effects on click through and buying rates. These are changes which get noticed because, for better or worse, they feed directly into the business bottom line. So with any responsive design, you need to be able to predict exactly how the site will change as the screen reduces in size.

Which is why having a clear underlying multiple screen size approach, delivered through a single responsive site is the best solution of all. Given the way the hardware is proliferating to a point where they will probably soon be a range of screen sizes from 3in up to 14in in one-inch increments, site owners will need to make their own decisions about the break points between screen size. When does a smartphone become a tablet? When does a tablet become a full size screen?

A responsive design needs to identify these break points, because the user will experience UI changes. A 'three screen' approach seems to be one now favoured by many existing responsive designed sites, broadly mapping to the original concepts of smartphone, tablet and PC screen.

There are some downsides of this 'one-size-fits-all' approach: Navigation can be harder to keep consistent when your navigation tools have to change to accommodate a small screen for example. Page weights are also under more pressure as the same scripts will need to load whether you are using a notebook or a small smartphone on the same URL. And if you are integrating other vendor services into your user experience, you'll need to check that their products and associated code is also compliant with a responsive approach.

So, by all means watch closely the quarterly shipments of tablets large and small, phablets large and larger, smartphones of all sizes and PCs. Feel free to observe the changing consumer desire for balancing screen sizes versus device portability. But most of all, be aware that mobile usage is still growing fast, and build your web strategy on a single platform capable of scaling across any screen size.