That's the Hales-Jewett theorem. The density Hales-Jewett(3) is a little different. Suppose you're putting X's on a 3x3x...x3 (n-dimensional) grid. Such a grid has 3^n points. What the theorem says is that if you've put X's on at least, say, 1% of the 3^n points, then you must have made a line somewhere if n is large enough. You can replace the 1% with whatever fraction you please, but that will change how large n has to be. No, the theorem doesn't state exactly how large n has to be, but already it's a challenging problem.

Terry tao's blog has an explanation that's about as simple as you're going to find. (At least one that actually explains the math without handwaving).

http://terrytao.wordpress.com/2009/02/05/upper-and-lower-bounds-for-the-density-hales-jewett-problem/

You get exp from engaging in RvR, so you can't stay at a particular level indefinitely. Not sure about T2 or T3, but at least for T1 there isn't much disparity from the best gear available and the gear an "average" player will get. It's pretty easy to get decent gear without really excessive grinding or spending lots of money. Also there don't seem to be anything like crusader enchants, which significantly increase a lower level character's power.