I realize that the comments here will largely be filled with people variously proposing that one do EVERYTHING with the iPad, and folks opposed to that. As this article is from 2007 and desktops are not extinct may I humbly suggest that a tablet device SUPPLEMENTS and COMPLEMENTS desktop and laptop computers running “full featured” operating systems (ones that allow you to manage files conveniently, for example, or configure the system as you wish it to be).
The question is not so much about processing power, but of form factors. A PCI(e) based audio interface is still superior to a USB one in latency and jitter, commodity RAM in standardized slots as an easy consumer upgrade, one can speak of the physical space required for proper USB ports if OTG and a zillion fragile dongles aren’t going to work for you.
The vast majority of content creators that I know, (including myself) use a tablet in conjunction with a traditional computer form factor. They use the tablet variously as a remote control, as an input device, and as a portable idea capturing device. It doesn’t replace a sound or video studio, it’s a welcome addition to one.