The MMO blogger Tobold has an interesting post about winning and losing. He's talking specifically about World of Tanks, but his point could just as easily be made about the SC2 ladder - specifically that ideally you should win only half of your games. If you win more than half your games then it's not because you are a good player - it's because the matchmaking system messed up - it's matching you against people who are worse than you. If the matchmaking system was doing its job properly you would win half your games.
Likewise if you lose more than half your games it means that the matchmaking system is screwed up and you are being pitted against people who are better than you. It's not your fault, it's Blizzard's fault.
For this reason, the removal of most people's loss statistic was exactly right by Blizzard - focussing on win percentage is meaningless. A person in bronze league might have a better win percentage than someone in silver. Does that make him a better player? No! Does it make him better than someone else in bronze with a worse win percentage? No again! The second player might be being matched against people in a higher league right before promotion. The percentage tells you nothing.
So why play Starcraft if not to win? Well, because playing should be fun, right? The act of playing itself should be a pleasure. Well for me it isn't. Laddering makes me nervous, and during games I am a mess of jittery tension and fear - "Shit! Better build a supply depot!", or "I hope he hasn't got broodlords yet - please please please!", or "If I expand will he just come crush me?"
I would never say I enjoy myself while playing.
So why play?
Part of the reason I play is that I want to get better. I like the feeling of improving - I sometimes look back at some of my games in bronze to measure how far I've come. But part of the reason is the same reason I used to do long distance running and competitive rowing when I was younger - the feeling afterwards. The period after the game where I grab a beer, kick back and watch the replay. I look at the profile of the guy I've just (hopefully) beaten, and keep my fingers crossed that he was in gold or plat. I watch the replay once feeling great about all the cool stuff I did, and then once again from my opponent's POV thinking evil thoughts like "Bet you didn't expect that drop, ha ha ha!"
That warm glow after the win is the main reason why I play. Which is why it sucks to lose of course!