Having teeth cleaned is quite common in kitties, and yes, they have to "knock them out" to do it. T & P have never had it done because the vet never indicated it was needed, but they have had only hard food their entire lives, which I know makes a difference. If you feed them canned food most of the time the tartar builds up a lot quicker - I guess because they don't have to "crunch" which would scrape the tartar away (but this is only my guess).

If you have any doubts, you could always get a second opinion, but it's not an uncommon thing and the consequences of not having it done definetely make it worth it.