Edit: Evita, it is not very common in the US for people to work while doing their MS/PhD. There are a few cases of course but its the exception rather than the rule. I guess that's why I assumed it would be the case with you.
I guess we have this system out of necessity, the government doesn't provide too much money for students and you have to live on something. And once you find a job, especially if it's in the same specialty you study, it seems silly to quit just so you can study some more even if you have some money saved