Taking advantage of glitches (ie Oghma Infinium) is definitely cheating. Taking advantage of exploits (ie free house trick) is semi-cheating. Think of it as illegal (glitches) versus unethical (exploits).

Technically speaking if you consult anything outside what NPCs tell you it could be cheating. Even if you have a strategy guide that you purchased it would be considered cheating by a purist.
Since this game isn't a PvP MMO the damage from cheating is minimal or non-existent. There are a lot of tedious things some people want to bypass because they want to experience the story and don't feel like trying to find out the Eagle-Dragonfly-Walrus-Walrus door code etc.

Some people ask about quest outcomes because they don't want to playthrough multiple times on one character by reloading a previous save. This game takes a long time to experience everything and not everyone has the time to play 100+ hours on 4 different character class-lesses so they take some shortcuts.
That being said: I've done most of these things (I actually have not looked up door codes yet - been close, but haven't yet).

Alas, I've even used the Ohgma Infinium glitch a little (just to get my Destruction up a bit so my weapons burn fewer charges - it was annoying, people!).
