Brute power not necessary!
A number of ideas here seem to suggest web developers need the horse power to do video analysises on their laptops which simply isn't the case. For the majority of developers most i5 processors are more than enough, although a fair amount of RAM is always useful. The reason for this is simply that IDE's + a browser are both fairly average applications and do not need that much processing power. Especially the fact that often faster processors come at the cost of battery life I would suggest battery life to be far more important than the cpu.
(Please note that I assume the reason for people asking for the i7's is mostly out of the concept that geeks (which most programmers) tend to want the best ignoring their actual needs (which is to some extend why apple and apple macbook airs are so popular: they create the best they can ignoring what the consumer thinks he needs (to best would be some balance between the two I guess)))