With regards to Walmart fabrics - we all buy what we can afford. I make a lot of charity quilts, and much of the fabric comes from Walmart. If it wasn't for Walmart, I probably wouldn't make charity quilts.
I also shop online and in the local quilt shops. I have found some of the same fabrics in the lqs as in Walmart, but for more money.
In the end, where you shop is and what you pay for fabric is a matter of preference and pocketbook.