It's not necessarily about the brand, more about the quality. The more expensive the purse, the higher quality materials are put into it.
Take for example Coach (a brand everyone knows) vs. say the average purse from Macy's ($35-50). Coach uses a genuine leather very similar to a baseball glove, something that holds true shape and lasts. A typical Macy's purse does not use genuine leather or uses a cheap grade. You can tell by the look, feel, smell, and the way it wears (pores).
Also, Coach uses a certain zipper YKK, the highest grade zipper you can use (will not snag, lock, break). The cheaper purses use cheaper zippers causing material snag, they break, and end up ruining the bag.
A good example of quality is a Louis Vuitton purse. Louis Vuitton has strived to make the finest handbags and leather goods for years, but what is his secret? A continuous piece of leather. No excess stitching and therefor the bag is more durable. I'm sure no guy has noticed this but Louis Vuitton has a special grade leather for its accents (handles, bottom, etc.) that changes color over time. It is superporous and picks up on the oils from your skin. You can easily spot an old bag over a new one just buy looking at the strap.
Think of it this way...
When you go to buy goggles, gloves, skis, outerwear, you buy something that:
a) has a good reputation
b) is made well and wears well
c) uses high quality material
d) is somewhat expensive
you wouldn't buy skis at kmart would you?