I sell A LOT of units (games) in the Android Market.
The 15 minute window has literally been a Godsend and has had no negative affect on sales at all.
I get far fewer people refunding minutes before the "refund window" is over AND I only received ONE complaint from a customer who thought they still had a 24 hour window a couple days after the new Market app went live.
You are still welcome to email the developer and ask for a refund if you don't like the game. I certainly refund money if someone hates my games, I don't want them leaving bad comments in the Market, and I don't want their money if they don't like my product, that wouldn't be fair.
"...where before I could buy something spur of the moment and then refund later that day if it's bad."
I believe this is exactly why it was "nuked". If it took you a couple hours to decide if the game is "bad", maybe it wasn't that bad and the ~$1 to ~$6 you paid for it was adequate for the time you spent playing it - whether you liked it or not.
When you go to an arcade, if you pump $3 into a machine, play for 4 minutes, and decide to get a refund, do you get it? Nope. The App Market is the new Arcade. BUT you get to keep the game to play over and over and over again for just a few dollars.
EDIT: I'd like to add that in-app purchases will be awesome.