also remember this isn't just for sellers. This is for the buyers as well. the commas can make it less confusing for them to see if a certain pet is 1 million or 10 million (for example). With that many digits it does get more difficult to see and verify the price at what it actually is. =)

it's not about practice. This is about making the game easier on the eyes. Not everyone has perfect eye function with squinting capabilities. I also don't think this is something that would be hard to do, since it's already incorporated in some areas just not in all, and would only benefit players. ;)