yeah, i agree... mastering can sometimes make a massively dramatic difference even when the original mix and source eq'ing is close to perfect, it is the mastering that makes a track sound warm and polished rather than crap...
the compression side of things is especially important - we generally find that this is by far the most time consuming part of production... it's not unusual to spend less than a day or just a few hours writing the track itself, and then spending days on the compression/mastering...

machina