Huh, so this is what the Steam Wallet is all about. Now that the individual Team Fortress 2 classes have gotten their chance to shine, Valve is moving on to the Mann-Conomy update. You’ll be able to purchase new gear with real money, like the Polycount weapon set, and trade items.
There’s a big ol’ FAQ with all of the juicy details, so I’d advise you to read it. The gist is that future (free) updates are still happening; this is an alternate way for devoted TF2 players to acquire some new gear. Additionally, it’s a way for community creators to get rewarded for their hard work.
Almost forgot — there’s a manly new comic, too. Grow a mustache, rip your shirt off, and read it.