When I got my iPad 2 over two years ago it pretty much replaced my laptop which was a 1st Gen MBP.
Not in power but in function and also does thing the laptop couldn't.
Such as for my purpose reading sheet music. Which can be done on a laptop but the iPod is so much closer to sheets of paper than a laptop as far as touch screen functionality with turning pages
The iPad also took over mobile entertainment from my laptop.
So I think having a iPhone and iPad is not redundant it just depends on ones needs when being mobile.
The power of current Mac laptops replaces in some cases the need for a desktop or iMac.
One could have iPhone,Mac Book Pro and iPad or iPhone,IMac, iPad.
Just depends on needs of the individual.