@uoq+1dZckW9r and others seem to be forgetting that pensions for new hires was cut-off back in 2004, so there's a huge swath of us that aren't subject to the silver handcuffs of a pension and that changes the dynamics quite a bit.
Those still growing in their career should be striving for those TA ratings, even if they're bogus in regards to actual skills. Those who want to stay here long term get the benefit of those indicating that they know how to play the game here and are willing to do so, and for those who will anticipating jumping ship later have it as a Gold Star that other companies don't know isn't about actual skills.
For anyone that hasn't figured it out yet, getting a TA ranking requires that you do your job at least competently and make both your boss and his boss look really good. On the flip side, being ranked as a poor performer requires you really screwing up and making your management chain look bad (or being part of whatever demographic is considered undesirable just before a year of anticipated cuts). Thus, it's a challenge to not just be an Achiever and get the same "merit" raise as everyone else, which is weighted to bring all of us back to the median salary.
And to tie this up to answer the question that started this thread, sure sounds like HR is fishing to get a feel of how many people are "stuck here"