The 20GB for the price of 10GB retention deal was pulled on the 23rd of October. It was a secret deal for people that were actually serious about canceling. It went viral and everyone and their mother was calling in to get it, I was one of them (and I got it). They decided to pull the plug on said secret deal, because too many people were calling in, even if they weren't serious about canceling. The higher ups realized that the deal went out all over the internet, and they were the ones that made it so the retention department couldn't use the code they used to originally give it to people, they disabled it. The ones that have it now, have it for good, unless they decide to change their plans at some point.
There were problems with it though. Some people have reported that they were changed to the 40GB plan by accident and were in fact charged for it. Which in return, caused a lot of people to flood retentions again to fix the problem and change them to 20GB, like they were promised. Only problem now is that retentions can only submit a ticket and have a higher up actually change it, since the earlier code was disabled.
I understand Palmbeliever, you feel entitled to something for free, a lot of us do. Sadly you missed the secret deal, a lot of people did, not just you. It happens. If you do like T-Mobile a lot better, why not just fully switch to them? I'm sure there are plenty of complaints (as with all other carriers) on their site, because everyone wants something for less, but nothing is free.
Kind of like how Sprint is offering 20GB for $100 and is waiving the line fees altogether. Sadly, as Geekboy was trying to point out, that deal is just a ploy to get people to switch. After 2015, they will start charging $15 for each line, like AT&T does if someone has 10GB or higher.
Also, T-Mobile does throttle grandfathered unlimited plans, but only the users they see that are abusing this plan. That's just the start of things though, because I am sure they will at some point throttle just to do it.