Actually...there is a difference...
Wal-mart fabric is called first run fabric..lower thread count and designs are painted on and since it is lower thread count they starch their fabric to hold up until you wash it...doesn't wash up well and shrinks more.
JOanns and Hancocks is called 2nd run fabric..a little higher thread count and colored a bit better...doesn't shrink as much as wal-mart fabric.
Designers get limited amount of fabric press time so they will do their first and second runs on these fabrics and then change what they want to change for third run fabrics ...
Third run fabrics are quilt quality fabric..fabrics sold at your LQS. These fabrics have a higher thread count, are dyed not painted and they have minimal shrinkage. Hope that helps you.