Dell and Gateway serve a lot of businesses, especially their line of servers and storage solutions. While working at college, all their departments run Dell servers. In the elementary school's, they run Gateway servers. I guess because of their reputation and the fact that they have support contracts that fit their needs.
Keep your Dell. They're ok PCs. I personally like their support and that was never a problem with me. I just hate how it comes DOA most of the time when we got them.
*Fact: Microsoft Window's Blue Screen of Death vs Computerforums.org's White Screen of Death. Which is worse?