I hear what you're saying. I take issue with "only" and "anything else."
The WeMo app I use to turn on and off lights or the Harmony app I use to control the media center? The reminders/notes app I use to jot things down? A video game that would have a 16:9 ratio on my television anyway? The babycam/security cam app that shoots in 16:9? The nest app? Spotify?
These apps would and do work just fine on a 16:9 or 9:16 display.
And, I could argue, media consumption is one of the biggest/most important uses of a tablet, so perhaps a tablet even *should* be 16:9.

(I actually don't care enough to *actually* argue it, but I could.)