I totally helped in picking out the ring. Although, we didn't have a "traditional" engagement either. We've been living together for 5 1/2 years and were talking about our future one day and decided that we should start moving toward the next step. Since my DH2B knows I'm very picky about jewelry he wanted me to have a say, which I didn't mind at all. Although, I'm sure I would've loved it if he had picked it on his own, but buying an E-Ring is a lot of pressure and I didn't think it was something that *had* to be a surprise.
Each couple is different, though. I think there is a general idea of what a couple is "supposed" to do, but I don't necessarily agree with that. Couples should do what is best for them.