As stated, it's all simply too peanuts to be an issue.
If an App sells for £0.79 then the govt takes 20% vat, even before Apple and the Developer share what's left. Add the fact that hardly anybody is will to actually pay for an App these days, not even a £0.79 App, they have to be free to get the downloads. So the dev has a load more work, building in a 'freemium' mechanism and/or working out how to incorporate sponsored ads. And then again, if you do get any income from ads, or In App purchases, govt's take their taxes, Apple take their cut. In the unlikely event the developer actually has anything left at all, there's always HMRC income tax (or corporation tax), etc, to look forwards to.
As a user though, I'm as tight-fisted as anybody else. My spend in the App Store, for iOS Apps, has probably not exceeded £15 in total, in the past 4 or 5 years.
@Mike, your bigger concern, having a smart phone where you hadn't before, might be the acceptance that adding data to your plan really is useful. Maps wherever you go, instant weather, browse the news when sat having a pint, access to your favourite forums.... you may be tempted. I'm not with EE, but most of the PAYG plans allow data for extra £few a month, that's amounted to far, far more than the app purchases.