Oops sorry for not answering before. What I wanted to say is that 4:3 has existed even before those tubes and was already used in early photography, so CRT limitations can't be the only reason behind the 4:3 aspect ratio. Also some guy had 2:1 CRTs in the late 1980s (I believe it was John Carmack or some other game developer), which is the reason of my "odd" reference.
I agree 1.5 has its uses I just always have liked 4:3 more and still believe the original iPad (including margins) is best form factor. It also seems weird that only 2 laptops/tablets seem to use the 1.5 aspect ratio so far.
Real Original thought is rare
I'd submit 4:3 in TV was a nobrainer, it naturally fit CRT tubes and followed earlier picture formats. however 4:3 on a revolutionary tablet was not so revolutionary and was a different kind of no brainer. Well in a way it was a nobrainer if you figure they intended it for viewing 5x7 & 8x10 photos. yes, not content creation or computer text and documents but viewing pictures. 4:3 actually sucks as a computer screen because it doesn't fit the printed page.
There have been many screen formats for theatre and movies but somehow 16:9 emerged as the optimal compromise and display manufacturers wanted to simplify and only make one aspect ratio to reduce costs. However that format actually sucks as a computer monitor because it also doesn't fit the printed page.
Finally someone with courage made a computer display that fits computer work. Hallelujah! Revolutions don't always take hold immediately and frequently there's resistance to change but resistance is futile, this format is here to stay.
You're free to keep using 4:3.