I think a great deal of people are misunderstanding what 'achievements' in the sense that Steam uses them are, they are, despite their name, not achievements. They are small badges, if anything. Their intention was
never to indicate how
good you were in a game.
Even one of Valve's flagship games,
Left 4 Dead, doesn't even use the achievements system as a measure of your actually performance (see
mine, for instance). The achievements are small goals that players are given, if they wish to fulfil them. While, of course, available for anyone to see, they are not intended and should not be used as a measurement of goodness of a player, for the most part. Okay, surely,
some achievements does indicate some sort of devotion.
Oh yeah, and by the way, this is purely a service that Steam provides, but nothing that's required. Many games on Steam has no achievements, but these games are often also available through other services. So giving the statistics of games for Steam is adding achievements, I am going with a 90%-100% that Firaxis are going to develop them into Civ5.
You may not be able to turn them off, but trust me, achievements are hardly annoying.
And yeah, achievements also vary in difficulty. Some are as simple as 'finish a game' (maybe even an achievement for losing a game!) to some really over complicated and difficult achievements. Not that I can personally think of what would be the most difficult to do in a game of civ right offhand.
Achievements are not here to replace anything. They are just an extra fun goal for those of us who are not part of a community or do not seek a hall of fame.