I think these days for new anime it's pretty much standard for it to be 1080p, but for older series there doesn't seem to be a standard?
Look at this: https://bakabt.me/torrent/154457/mahoromatic-automatic-maiden-bd-720p-joseole99
Some guy in the comments says the raw provider changed the resolution from 1280x754 to 1280x720 to remove the black bars at the sides of the screen. How could I know the original aspect ratio without owning the DVD myself?
This is unrelated, but1280x754 seems like a random number that doesn't fit on the screen, so why did they (anime studio) choose that resolution? The only thing I can think of is that tvs used to have that resolution back then, in japan maybe.