There is a difference between "not supported" and "won't work". Just because the manufacturer of the product (D-Link) does not officially support Windows 7 with that product, doesn't mean that product won't work. This is especially true when the product uses a third-party chipset. D-Link may not release drivers for their product specifically for Windows 7... but there is nothing stopping the chipset manufacturer from doing so.
Also, different employees may have different opinions. You'll get those that say because there are no Windows 7 drivers available, the product will not function. You may get another that actually knows a little more and they'll tell you that while they don't officially support it, it does in fact work.