I never watch cams, but I've looked at the member cam thingy and been half tempted to have a look.... I didn't though, for me images get far to imprinted on my mind, once I see a dick pic it'll always stay with me, occasionally flashing in my mind... very disturbing when I'm trying to concentrate or do something normal. And sometimes is enough to fuck up my libido. I personally find looking at random penis's more on the side of disgusting than arousing... Strange as I love cock... but I guess I only like to see those of my choosing... But I know that there are models who genuinely like watching cams.
Maybe it's out of boredom, maybe out of curiosity, I think it's fairly safe to assume that in most situations there is a hope in their mind that you might spend tokens on them, even if it's only a distant thought and their main focus is just having a look.
When I've been tempted to open random member cams it's not for sexual reasons... I'll be honest, it's more because I've wanted a bit of a giggle/something scary to look at.
I also don't think this will stop members tipping for girls to view their cam. Some guys are ultimately obsessed with being watched. It's a fetish. Even if they like and watch a girl, if she doesn't watch cams they won't tip her because she doesn't fulfil what they want. It's kind of like if you like tits, you can see fuck loads of tits for free, but it doesn't stop all people tipping for them. I mean sure it does stop most people tipping for them (imagine how many people would pay for this stuff if they couldn't get it free), but there are enough dudes who will still put money towards it. It's the same with people being watched on cam. If they want they could go to chat roulette or something similar and get watched for free, they are choosing to go to camgirls. Some are freeloaders and try to get girls to "open cam bb" for free, but as far as I can tell most are willing to tip a bit, though the price of watching cams is usually pretty low, so if it is a guys fetish then it's not an expensive one.