Call Blocking -- Why can't we do it?

Question

The simple question is, "Why can't we have an app or option to block unwanted calls, without jailbreaking the device?"
Some of you are going to say, "You can through your carrier." This is only partially true.
Verizon allows you to block 5 (just 5) calls via their website. But why have to go to their website to do this? What if you have a company-paid line and don't have login access to their site? Why do you have to renew your blocked numbers every 90 days?
My Blackberry Storm had an app that simply intercepted the call and dropped it or directed it to VM, if I had put the number on my block list. Blocking the contact was a simple as selecting the number from the incoming call list and choosing, "Block this contact" from the menu.
This seems to be related to the lack of flexibility in how calls are received by each contact. There are no separate controls for volume and vibrate that can be set per contact. If there were you could turn off vibrate and silence the ringtone for contacts you didn't want to be disturbed by, at the very least.
Had I known this simple functionality was not available I would not have bought this phone.

Answer 1

Thanks for the replies.
roaminggnome: I know it's not a feature. I am lamenting that very fact. And, yes, it was a great feature of the Blackberry (and others). Why does Apple not allow it? There has to be some business reason because it should be easy enough to accomplish if apps could intercept a call before it alerted you.
I also know that true call blocking is a carrier-level function. Wouldn't it be great if you could block the number on your iPhone and the option was saved on Verizon's server? Why not? Aren't smart phones supposed to be smart? I can easily block calls on my home phone through AT&T's U-Verse service.
Instead you have to jump through hoops to create a silent ringtone (or buy one). You have limited SMS tones to choose from and people talk about jailbreaking their phone just to add more. This was all easy and free on the Blackberry.
The Google Voice idea would be great if my true cell number weren't already out there. I really don't want to have to change numbers and have to redistribute it to all who should have it.
I really thought the iPhone would be like the Mac, with lots of cool options and functionality. I've had Macs since 1984. I may have been mistaken.