Can't hurt to take it in, but obviously a mashed screen is in no way covered by warranty so if they do replace it free, be very thankful.
If you need to repair out of warranty ($199, assuming USA) then you have the option of buying AppleCare+ on the replacement for 1/2 price so for $249 you'll get a new phone and AC+.
You mean $149 ($99 for AppleCare+, plus $49 for an accidental damage replacement), right? Which is, as you point out, cheaper than one out-of-warranty repair ($199), plus you're covered by AppleCare+ (which includes one more $49 repair) from that point on.
I think that AppleCare+ for the iPhone 4S was Apple's way of firming their policy for accidental damage. They were fairly generous in the past (they replaced my dropped & cracked iPhone 4, gratis, "just this once"), but I think the whole purpose of AppleCare+ was to provide a reasonable alternative somewhere between giving away free phones and charging $199.
We know that Apple's intent with AppleCare+ is that you buy it before the damage occurs. They tried to require you buy it at the time you purchased your phone (and wouldn't be eligible after that), but since that was logistically difficult for some they offer a 30 day grace period -- meaning you can buy AppleCare+ any time within the first 30 days of phone ownership. I suppose there would be no way for them to know if you broke your phone in the first 30 days,
then called them up an bought AppleCare+ (you can - or at least could - buy it over the phone [I did], but at one point they were trying to require you to bring your phone in for a physical inspection to make sure it wasn't damaged already - I don't think they're doing that now though).
Bottom line: you could always bring your phone in to the store and ask, but don't have high hopes. Signs are they're specifically trying not to give away free phones to replace phones damaged by the user anymore. If you're within 30 days and don't mind some dishonesty, try buying AppleCare+ and then claiming you broke your phone right after.
Incidentally, I received my phone (from AT&T, who didn't offer AppleCare+ with purchase) on launch day and immediately called Apple to buy AppleCare+. They couldn't sell it to me that day (due to overwhelmed system, as I recall), and while talking to the guy about the new policies he told me they were already trying to deal with the phones that, for example, didn't make it out of the parking lot before they were dropped and broken. We talked about how, with thousands upon thousands of units moving in one day, some percentage of them are going to get damaged. They've heard it all.