Why do searches come up with secondary domain name pages?

If you do a search from Yahoo! for refurbished axxess, my site comes up number 1,4,5,6,9,15,16,17,19 AND 20. Of all those links only 2 go to our main domain, www.mainresource.com. The other ones go to our secondary domain names, like www.mainEresource.com, www.mainresource.biz, etc.

My question is, why, if all those links go to the same site (which they do, they're all duplicate), would it display our secondary domains, the ones we don't really promote? When I do the same search on Google, we come up #1 and there is no reference to those other domains, just www.mainresource.com

Second part to that question is: if I get rid of those secondary domains (I don't want to get banned by search engines for having duplicate sites), will I not turn up in the search engines as I do now?

Thanks!!

if you remove your duplicate sites the only way it could effect how you appear in search engines is if your duplicate sites link to your main site but i wouldnt have thought your search criteria is that competative so it should effect you to much