I agree with both of your points 100%. I run a bunch Numbers spreadsheets on my iOS devices right now, and it is really cumbersome on the small screens of iPhone and iPod Touch.
BTW, I've been kicking around the idea of iPad3 and iMac replacing my MBP. The iPad3 portion will happen soon enough, but the iMac won't happen until the MPR is no longer operational.
I find little satisfaction using the tiny screen on the iPhone 4s on much more than occasional use. Like you, spread sheets are a large part of what I have to do and doing them on my iPhone would make me HATE it.
I love the iPhone, iMac and MBPro and use them all, but they each have their place!