Is it odd to have three colon polyps removed during the same procedure, or is multiple-polyp removal common?

No. It is not odd to have several polyps removed at the time of a colonoscopy. The intent is to remove all polyps found unless you happen to have familial polyposis in which case there may be thousands of polyps and obviously they can't all be removed.
Not really. It isn't, however, necessarily a good thing, since it shows that you are a polyp-maker. This may increase your risk of cancer if you are not followed properly. Usually 3 or more polyps means you should have a repeat colonoscopy within a year or two.