There is a theory I have forged regarding the ranking potential of different domain extensions, specifically between the ".com" and the ".net", ".info", ".org" and the various other domain extensions, based on experience and some research. It would be wonderful if I were to find a specific interview about this with Google or Microsoft, but nothing seems to have been published or suggested in an interview regarding the matter of different extensions.
However, I think the .nets, .orgs, .cos, etc. only seem to rank lower than the .coms, because the .com domain extension has become an internet standard for domain names, meaning there is probably a far larger pool of .coms than all the other domain name extensions combined. This means that it will be far more likely that a webmaster with the .com extension will "out SEO" another webmaster with a different domain extension, simply because there are more opportunities for the .coms to do so. I have occasionally come across the odd extension that ranks on the first page of Google, sometimes the first result for certain keywords, but nothing definitively suggests that these extensions will rank lower.
The .com domain extension has been around a lot longer than many of the newer extensions available today. This means that they have the advantage of domain age and mature SEO that the others do not have right now. However, if more people begin to use the more obscure extensions, I bet we will see that change.
If you think about it, it would not be very fair for a search engine to favor a site based on something as inconsequential as the domain name extension. There is no benefit to it, so I highly doubt this is the case.