Dating Dilemma - Bootie Calls

So this is a fairly solid outline of how the last couple of weekends have played out:
Friday night: 
-Go to a bar to meet up with friends/celebrate somebody's birthday
-Meet cute 20-something
-Have great conversations, joke, flirt with 20-something
-20-something asks for my phone number
-I give him phone number
-We hug and part ways
Saturday night (somewhere between 9.30 pm - 11.45pm):
-Cute 20-something sends me a text message: "Hey, what are you doing tonight?  Wanna hang out?"
-I respond with (fill in the blank), "At dinner/movie/hanging with friends/sleeping"
-Cute 20-something replies, "Wanna come to my place afterwards?"
-Me: "No thanks. I'm kind of exhausted.  How about later in the week?"
-Cute 20-something, "Yeah, I'll call you later."

A week goes by, I don't hear from the 20-something and the cycle repeats itself with a newer, cuter, flirtier 20-something.
Seriously, what is it with 20-somethings and bootie calls?  It seems that when you meet a guy who is still in college, the next time he speaks to you, he asks you out for dinner/movie, in other words a proper date.  When guys in their 30-40s want to get together, they ask you out for drinks, coffee, or something that doesn't consist of a lot of time so they can get a feel of the situation, but bail if its not working out.  Clearly, 30-40 year olds have all figured out that a bootie call to a stranger doesn't actually work.  But what is going on in the heads of the 20 year olds?
Just so none of us has to think too hard about it, I polled a couple of males for their take...here is what they had to say:

BS: Generally when guys do this, they are playing the "hard to get boyfriend-wise"card... "If I make her think I'm only in it for the booty, then the pressure's off when it comes to dates."

RH: "It's just age.  Guys thinks more about just hooking up in their 20s.  Between 30-40, guys still think of that but perhaps become more selective of who they will spend time pursuing.  As I've somewhat matured, I'm more inclined to try wining and dining someone then just making a booty call."

BB: "He's probably like 'hey, this girl is in her 30s now, she probably doesn't want to mess around with any dating, and I might get some sex.'  I don't necessarily think that this is the prevailing wisdom of the current 20 somethings...although, does it work?"