Let me see if I can answer this one....
When you're watching TV and someone moves in front of it and blocks your view, what do you do?
You tell them to move out of the way. Same thing with sites. A lot of sites are popped up... if the surfer doesn't have his/her browser maximized, they're not going to see the full monty.
So the site can do it for them. You know how fickle the surfer is: if your site loads in a screen that's minimzed completely or by 50% or whatever, boom, there goes a potential sale. It's hard to sell something if you're only advertising a corner of it, lol.
Using j a v a s cr ip t to retain focus on a fully maximized window is another thing. I agree, If you have a popup or for some reason your site blasts itself to the front and maximizes itself, well, that's another story. But if they're going to your site anyway, no harm in allowing them to view the whole thing.
And by the way, the majority of surfers don't have a dual-monitor setup..so I'm not sure why you're comparing your experience with their's. For the same reason, site owners design for surfers, not Webmasters....
