Ratings and (white) first move.

Chess rating systems Elo, Glicko(2) and Trueskill state that when two players of equal rating play that their win/loss ratio should be 50:50. Or put another way if I play an opponent of equal rating I have a 50% chance of a win (ignoring a draw). I can understand this but it does not take into account the first move advantage which should tip the win 2-5% in my favour. Can someone please explain why the rating systems ignore white advantage.

Let's look at it differently. Computers give White advantage a 3/10ths of a pawn advantage ( or nearabouts) in the beginning.  If this were an endgame position, the score would point to a draw and the computer (well most of them) would concur with the "=" symbol.

With that being established, I would say that the slight 0.3 advantage that you alluding to really doesn't matter ... and statistically evens out as a player plays tons of tournament games. I am a TD and I notice that the pairing software makes it a point to ensure than each playter gets black and white an equal number of times with very few exceptions.

Not really answering your question, but throwing in a few observations.

I have noticed that playing with White (with even the 0.3 miniscule advantage) tends to matter more when GMs play...perhaps your question would be better suited for that level of play. At the amateur level, the advantage of being White gets even-ed out as the number of games tends to get bigger...atleast that's what I think.

The rating system ignores it because over time you'll have white as often as you have black, so the effect averages out.

0.3 pawns? I don't know what computer you're using to get that much of an advantage.

And yeah, you get an even number of Whites and Blacks, so it evens out over time.

With best play on both sides, the game will be a draw.

I dont think theres much difference between white and black below the elite level. I sometimes do better with black pieces than with white in my tournies.

The Steinitz's theory of equilibrium is right or wrong? I always wondered about it.

He's right that chess is a draw, and that if both sides play perfectly, neither side can win. This hasn't been proven, but it seems more or less everybody believes it.

Where I think he's wrong, is that he says that you need to have an advantage before you can start an attack, otherwise the attack will fail and thus you will have a disadvantage. I think it's perfectly possible, with both sides playing perfectly, for white to start an attack, with black defending and the game still ending in a draw. But, of course, only if the position is such that an attack by white is called for - let's say, in a mainline Najdorf.

But then, he was writing at the end of the 19th century, when everybody started their games sacrificing pawns for wild attacks. He's basically saying that an attack needs to be based on something :-)