It seems like you are playing a bit fast and loose with some of your claims, to stack things toward Verizon. For example, it appears you get some type of discount with Verizon that makes your plan $145.
From what I see, the Verizon plan you are talking about (a 4GB shared plan) costs $150 for two smartphones, and the T-Mobile plan is $100 for one line with Unlimited service and a second with 500 MB. I'm assuming the reason you are claiming $110 for T-Mobile is including tax and that your discount is taking your Verizon plan to $145 after tax -- but it doesn't change the fact the actual plan cost would be $160+ for most people -- and that type of price difference gives T-Mobile a clear advantage.
The other thing is you appear to be basing this off of "power users" -- and we, who are on this type of forum, are the minority of most Americans. Most people don't buy a new phone when it is first released but will typically wait for it to be on "sale", not to mention they typically don't change their phones every 2 years (most people I know aren't even sure when they will be eligible to get a new phone). It also helps that you fit almost perfectly at the 4 GB cut off that Verizon has -- if you needed 4.5 GB, or 2.5 GB, suddenly that would again, even with your discount, tip the scales back to T-Mobile.
I will agree that one size does not fit all; IOW, T-Mobile is not the best choice for everyone. The fact remains though, for many Americans they do offer significant savings, particularly over AT&T and Verizon. It just all depends what type of phone user you are.