Haskell Platform feels a bit like Prelude; fine for people who are just using it for small self-teaching projects, but once you're supposed to do something "serious" then people seem to throw up their hands and say "No! never mind that.". I don't know. Maybe I've got the wrong impression.
Now that I know enough cabal to get by and not screw myself over (by creating dependency hell), I feel like Haskell Platform might not be relevant to my needs any more.
No, you're perfectly right. And while HP may be up to date right now, it'll be out of date next month and it will keep getting more and more obsolete until the next release in a year or so.
"I realize this one was a long time a'comin'. I take the responsibility for the decisions that lead up to being this late, including deciding it was worth it to wait for GHC 7.8, and that this was the right time to re-write the platform build system. I hope the speed that we can now turn the platform will be evident in future releases."
The issue is that platform packages are in the global package database, which doesn't play well with the (amazingly useful) sandboxing that cabal provides. And may cause other problems too.