I have had a look, and surprisingly, it looks like this has never been suggested before as it is something that I find very annoying.
When you are drawing a line, it often takes a bit of effort to get it to go exactly straight, this means that I end up spending quite a bit of time just trying to straighten up the line, instead of working on my creation. If we could have something so that lines would never go 1 pixel off the standard 90 degree steps it would help a lot. As for if someone wanted to make something that would go 1 pixel off...really, have you ever had to make a line like that, because I haven't. If they really need to do it then they can just draw two lines. If someone REALLY decides that they MUST have something that will go 1 pixel off then we can put an option in I suppose.
Anyway, I think this would speed up making creations a lot.