Hrqls: I'm not sure that players should feel obliged to play anyone but those they choose.

The meaning of "rating" is the relative difference in success (as opposed to skill) between a player and her/his opponents. If two people only play each other then their ratings will completely accurately reflect this difference between them. It wouldn't be possible, however, for those ratings to be meaningfully compared with any other rating within the ranks of that game type. The same applies but to a diluted degree if a player restricts themselves to a small group of opponents who may pr may not play more widely themselves. That's the issue that I think Fencer is looking at and it's a fair one from the game pool/rankings perspective.

But I still feel that a player's choice of opponents ought to be governed solely by personal criteria.