4:3 video has 720x480 resolution
525/60 digitized SD video according to Rec. 601 is indeed 720 pixels wide, 480 pixels high, including some blanking on the sides. Digital equivalent of 625/50 is 720x576. In both cases, frame aspect ratio is 4:3, this simply means that the pixels are not square. See https://en.wikipedia.org/wiki/D-1_(Sony)

To make matters more complex, only a subset of the frame has 4:3 proportions. I believe, only the 704x480 (for 525/60) and 704x576 (for 625/50) has 4:3 proportions. See discussion here: https://lurkertech.com/lg/video-systems/

So, 480 pixels are 10/11 in proportion, 576 pixels are 59/54 in proportion. Also see here: https://en.wikipedia.org/wiki/Pixel_aspect_ratio And do not forget, that both 480-line and 576-line formats can also be widescreen (16:9) yet having the same number of pixels per line! Plus, numbers like 59/54 are not easy to work with. All of this caused that for 576-line format pixel aspect ratio has been chosen as 12/11 for 4:3 screen aspect ratio, and as 16/11 for 16:9.

Square pixels became the norm starting from VGA video adapter I believe, and then from HD specs for 720-line and 1080-line video. By the way, there are some HD formats that record 1440x1080 or 960x720, yet having 16:9 frame aspect ratio, they also have non-square pixels. Square pixels are relatively recent development and should not be automatically expected.