Or maybe not...
Well, that's one side of the argument. I have both an iMac and a MacBook Pro. The iMac sits on the desk by itself most of the time, well the MacBook actually gets used. Unless you're planning on doing things like serious video editing, for example, which is probably better done on the iMac (but NB the caveat "serious"), there is pretty much nothing you can do an iMac that you can't do on the laptop equally as well -- but the reverse is simply not true. The flexibility of a laptop just can't be beat. Yes, an iMac screen is bigger, yes, it's faster, but unless you're doing really graphic- or processor-intensive operations, that's a distinction with no difference. Think of how and where you might actually want to use your new computer before you come to a final decision.