And that was certainly one of the reasons they brought up.

That's less of an issue of technical possibility, though, and more 343i being all "we don't really feel like paying a team of software engineers to spend a year reconstructing Halo 1's engine around an asynchronous networking model."
They probably would have gained more sales that way, but maybe they decided it wasn't worth it. Who knows.

But the really annoying thing about their argument is that it acts like people in the community don't understand that latency, bandwidth, and other connection issues exist. "Oh, it'll feel different online." As if we didn't already know, from a lifetime of experience, that every game ever feels different online.
Hopefully Fourteen Day Buy and Play succeeded in permanently shifting their public relations away from "let's treat our customers like complete idiots".