Let us go back a bit farther as to why 4:3. That, was where film started, and computers went along for years, until the movie industry decided that its goers needed excercize and created wide screen so you would bob back and forth like in tennis. Besides they all sell something perfectly good out to sell something new to make money.
It is important to consider what you are going to use the Touchpad for. I have two laptops, one soon to go, and the one I prefer is the one with greater vertical resolution. If you are only watching movies, then wide/super wide is a better choice.
I do not think that the tablets in general are primarily for movie watching. I plan to use mine around the house for email, reading, browsing, and looking for movies that I will watch on my 65". Yes, occasionally, it will show a movie or tv, but that is not its purpose.
Yes, if HP copied Apple on 4:3, it is because both Apple and HP saw it was the best of a lot of worlds. And it may have helped that it was a properly priced technology already in stream. Sorry for pun.
Tablets in general are a supplement device to desktops as are laptops, which are movable desktop replacements. Tablets are casual, much more portable, and will serve many new purposes. Recipies in the kitchen, manuals under your car, relaxation in the doctors office who has no new magazines, quick email and sync, showing a slide show of your grandchild, reading emails while you are away on business and a laptop is a heavy pain on the plane. You will always do far more with a big screen TV or computer than a tablet, that is until the next device comes along. But a tablet has a real purpose.
And 4:3 is perfect at this time.
I am waiting for wrap around glasses with imax [d^mn I dislike that i] and octophonic sound with a transponder on my spine for movies. Meanwhile, I plan to make great use of my 4:3 Touchpad.
Over analyzing technology, especially with prejudices, makes you forget that new money is a major driving force, and technology is rushed out to sell the need, not to fill the need.