This site consists mostly of Nintendo fanboy types, but retailers generally don't choose to deal in only one system. And buying from the sponsors has several benefits:
They're as trustworthy as anybody that you'll find as an online store. Otherwise people here would complain and they would probably be dropped.
You're helping this site by proxy. Keeping those stores in business keeps this site in business. Everybody on this site constantly touts dealextreme despite their failings, yet this site doesn't gain anything from their success. I perceive a lack of priorities in this tradition.
After you're done buying, you can write a review in the reviews section about it and promote the fact. Nobody needs to hear about dealextreme because we all know that the shipping is slow and their customer support is lackluster. Dealwoot used to be a sponsor and I bought some screen protectors
as a result, and the cost was easily comparable to dealextreme and the quality was great.