Games are certainly relevant but in building the business case for participating in the app market in general it's crucial to keep in mind that all these sales statistics pertain mostly to games.
And while I certainly don't consider $2bn irrelevant you have to admit that the hype around app sales is currently far out of proportion to its economic significance.
I've not seen any figures that suggest that they're "mostly" games - can you provide a link (the one below doesn't support mostly, it support games as the single most used but by a relatively small margin over several other categories).
I'm not sure it is just hype. Digital music is considered significant yet app sales are about to outstrip downloads and there are predictions that if game downloads carry on on their current trajectory then in 10 years time Apple IS mobile gaming.
And apps are an enabler for a lot of other stuff from smart phone sales (for instance that $2bn includes nothing from free apps such as Facebook and Twitter which are key for many people) to data sales to add sales (estimated at another $850m by 2014) to everything else.
Sure, on it's own $2bn can be seen as relatively small beans that's not the full story for revenue that can be directly attributable to apps and there are significant indirect effects beyond that.
And while I certainly don't consider $2bn irrelevant you have to admit that the hype around app sales is currently far out of proportion to its economic significance.