Check your display driver's settings.. Normally its set to a default (balanced) preset.. Check to see if yours is set on "Performance" or something, coz that would set everything on the lowest quality settings in games so that you can achieve best performance...
If you set it to "Best Quality" or whatever, the default quality settings in games would be higher.. Also some of the new games auto detect the "correct" settings, so ensure that you drivers are up to date to ensure that this feature works properly...