I think it all depends on what you use a laptop for, remotely, as to whether you can get by with just an ipad. And throw in a keyboard of some sort, and the differential gets even smaller. Throw in the vastly more powerful imac that you could then control remotely...
That said, I wouldn't recommend it for most people, just people considering a 17" laptop. After all, those things only vaguely count as portable.
The only mac laptops I'd recommend for anyone at this point are the macbook airs and the retinabook, depending on use case. I've used my 11" macbook air as my primary computer for 1.5 years now (first a 2010 and now a 2011), and couldn't be happier.