I'd expect that they would want to tell the truth because they'd make more money from selling the higher tier product.
People at Best Buy have to deal with a large number of products and not just Halo or even just video games. I'd imagine the person had a different specialty than you needed. So if you were talking to a person at the front of the store and not in the software section, I suggest finding someone in the software department next time. Also, the halowars.com website here, as well as the xbox.com website had accurate information. I'd suggest trusting the official information from the developer and the manufacturer/publisher over the retailer rep next time. Hope this is helpful.
A Halo Wars Story: Once upon a time, there was a light bridge. On that light bridge, there were many covenant. When the UNSC turned the bridge off, the covenant fell. The End.