Well I guess an ocean liner and a yacht are both boats, and based on the logic in some of the posts, the yacht could do everything an ocean liner could. Oh what the heck! Lets throw in an aircraft carrier and tramp steamer ... they also must be the same capability wise.
And of course trucks are the same as limos ... and so the argument goes on ... yadda yadda yadda! Get real!
Try opening multiple tax spreadsheet documents with 10 or 12 page width entries, and columns 30 or 50 pages deep ... simultaneously with the tax dept online lodgement service also open ... on a 10 inch or even 15 inch screen. Good luck!
Portable devices and desktop devices are designed for totally different modus operandi. The first need to be small for convenience of portability. The latter for convenience of large scale work where portability is not an issue. If I'm sitting at a desk 5 days in a row working, I don't want to have to plug a portable device into a monitor every day. In addition you can't personalize portable devices or repair them as easily as towers.
Try putting 3 SLI linked graphics cards, 30GB RAM, water cooled CPU, 3 DVD burners, 3 internal SSD HDs, 2 USB external HDs and an eSATA HD ... in an iPhone or tablet or laptop. And no, I'm not talking a gaming machine. Just a very, very fast machine capable of serious multi-tasking.
The onboard graphics of my friends expensive Sony laptop recently carked it, and the mobo had to be replaced to fix it, making the cost prohibitive.
You can kill an elephant with an elephant gun or you can starve it to death. Both methods achieve the same result. One is a tad quicker than the other.