There are exceptions:
hosts - Resolves IP addresses to host names in lieu of DNS
bcd - The boot database for Windows NT6-based operating systems
ntldr - NT Loader for Windows NT4 and NT5-based operating systems
I'm sure there are a few others out there. 
Well WHEW! thank GOODNESS we got that mozza ball out of the way. The fact that there was a single slightly inaccurate fact present here was really eating away at me.
besides, every file DOES have an extension. in the cases specified it's simply an empty extension. Technically the hosts files name is "hosts." (with a dot on the end) but ever since MS-DOS it's been allowed to exclude the period separator if there was no extension.
For example, if all files didn't have an extension- why does
dir C:\windows.\system32.
give anything back?
Sure, they are <empty> extensions, but they are still a part of the filename. Going by your logic, the fact that you can create a file called ".dat" (with an empty basename) implies that files cannot have basenames. Additionally, it means that you are implicitly saying that a file can have no filename and no extension. But we know that is not true.
For example, the . and .. directories are perfectly valid filenames- . is a directory with an empty basename and an empty extension. Sure, most people simply say "no extension" but this in and of itself is simply saying that it's an empty extension, not that there is no extension. much as if somebody saying "we have no apples" doesn't imply that there is no apple tree.
Summary: if your going to overanalyze what people are saying and make uncouth and off-topic observations based on some innate need to "set the facts straight" make sure that you are in fact setting them straight yourself.
