It doesn't matter if they're easily excessible; they still spoil a lot about the game. Just look at any of the stuff from the bungie manuals. They talked about Balor about the Fallen Lordsall sorts of stuff which is supposed to be delivered as the story progresses, not spoiled from the beginning.
I didn't read the TFL one at firest because I had just borrowed the CD from a friend. I read it later only to find all sorts of spoilers and stuff about the game I had no way of knowing without playing the game to the end (stuff which talked about the ages, the cycle, Balor, The Leveler, and a bunch of other things we take for granted). Therefore, I was sure not to read the m2 manual until I finished the game. Same thing was true there, though perhaps to a slightly lesser extent. Playing with the m2 units on TFL via Magma before I got m2 was also very, very spoiling of the fun of the game. M2 was bad enough without its graphics and units already known to me
So I'm one of those people who doesn't like any kind of spoiler. Sue me :-). At least say "potential spoiler" for those of us like me.