There are two sides to this "coin". For example, here's a link to a news story about one Petco being cited for animal abuse (note, the citation was not for what the original poster was talking about).
http://www.sonic.net/~melissk/petcocit.html
This next article talks about Petco (and other stores) donating large quantities of food, toys, and other merchandise to animal shelters.
http://www.bayweekly.com/year00/issue8_21/lead8_21.html
The PETA site is unreliable at best. The original post smacks of urban legend-ism.
Ulrike