Yes, for some time (the dark ages I like to think) programmers had to sacrifice productivity to make things faster, or to make them fit in memory. The original C compiler had a 6 character limit on variable names, leading to abominations like `strstr()`.

Fortunately, by the Pentium era, which was when PHP was designed, those times were long gone.

"X made this design decision before us" is never a good justification for any design decision unless the decision is truly arbitrary (i.e., are arrays 0 or 1 indexed?) -- then it might be better to stick to what's more familiar. If it was a good design decision then, then there must have been some reason at the time that should be true now to give a good case for repeating a design decision.