W/D/L is a silly stat becasue it doesn't take into account opponent skill and lobby games aren't meant to be "serious". I often use national decks in lobby games, for example, and I'd hate to have a W/D/L stat hanging around my head for these games when I'm not really trying very hard. Much better is Elo. I'm not really sure why more people don't play ranked games to be honest.
Because it's sometime hard to face the fact that you suck. Blizzard understood it with elo arena in WoW, so starcraft II is in League for ranked games.
But I agree, elo tend to be more representative of the skill.
A player saying "gl hf" at the start of the game frighten me much more than a lvl 59. (It's the "gl hf" curse. most players using it are skilled players, and only a "u2!" can save you from an horrible defeat !)
Also... You might have fun playing against a clan, or joining one for that matter. If you're really that frightened I guess we'll just have to deactivate our clan tags... Will that help?
I have a main clan [FFR], but when people are leaving because seeing too many of us in the same team, I've got also a secondary clan where i'm alone [Aime les poneys] (dig ponies), to make people less scared.
And honestly, i sometime join clan battle because most of the team what clan do is brainless rush with teamspeak. With a little communication with your team during the deployment phase, it's not THAT hard to win such games. (okay, your mate have to be at least a little skilled. For example "herp full arty derp" is useless in a team.)