It's not that they are adding it, it just comes with the technology. Verizon would not be able to just add something to each CDMA tower to enable data while on a call because that signal technology just can't "multitask" (every time I think of that word I think DRRROOOIIIDDDD. Damn you Verizon marketing).
ATT and VZW are both moving to LTE, don't think someone has explained that yet in this thread. This poses a new question: Will you be able to roam on ATT's network if you don't have a VZW signal?
It's not a happy coincidence that they're including the simultaneous data/talk with LTE. Verizon certainly has the ability to not include it when they switch to LTE, or they could even charge for it. They're going to include it because there are a lot of folks who wish they could multi-task instead of having to hang up the phone to do something. Which, unfortunately, is just like dial-up internet.
If someone said "I'm on dial-up, and I have an incredibly awesome hard line that never hangs up," I don't think anyone would say they were "leading the way". On this they're not, which stinks, but I'm still glad to be on Verizon.
Actually, my feeling is different in regards to what you think they are doing. GSM standard is actually one that the Europeans designed as their implementation for better Cellular service. Whereas the US had, prior to CDMA, TDMA analog system. If you look at this:
IS-95 - Wikipedia, the free encyclopedia
This talks about CDMAOne, the 2G implementation that Qualcomm created which is the basis of the current CDMA2000 (CDMA 3G) technology that majority of North America uses, but not currently used worldwide. The GSM standard was adopted by many countries, from what I recall, due to a lack of ingrained infrastructure like how AT&T/Verizon(GTE) had with most of North America, the GSM standard was easily adopted to provide phone service. (Also the fact most of the European countries and Asian countries have lots of cities that are historical in nature and did not build up a telephone infrastructure the way America has since its invention the way America has. And no, this is not American elitism at work, just simply the US had less history in comparison to other countries and had the technology on hand to build cities with it versus retrofitting many more cities that didn't have it.)
The reason AT&T and T-Mobile GSM sucks so horribly is the simple fact that in the US, we never adopted the GSM technology until AFTER its popular adoption in the other countries. And what has hurt us more is simply the fact that CDMA was developed at the same time as the GSM, but was adopted early and infrastructure put in to support it.
If you bother to listen to the Customer Service stuff for T-mobile and AT&T with regards to coverage, they are working to put up more towers to do so, however, that is dependent on how strong of a market in certain areas are and where they can put up towers to cover those areas. GSM has a much stronger presence in the Euro/Asian countries because they were able to setup towers and such much easier for their cities and designs, where as the US relied heavily on the TDMA infrastructure first and CDMA, while expensive, was an easier conversion over than the GSM.
Also, Verizon does make one additional proviso over what GSM providers in the US don't provide... Backup support. Case in point, power outage in my area due to the Fires knocking out power in Santa Barbara (3 major power lines coming in, 2 of them happen to be in the fire area), Verizon put in battery backups to carry their towers, the GSM providers did not. People who were not on traditional land lines or with Verizon suffered the most due to lack of power.
At this point the issue is less about technological leads, but simply what is going to functionally work for the situation. While again, it would be nice to talk and web browse at the same time, and the LTE network should allow Verizon and Sprint to do so now, the other thing that comes into play is also the tried and true debates like VHS vs Beta, and Blu-Ray versus HD-DVD... Some technologies people don't rush into because of how one is better than the other, but eventually one will win out. And mind you, AT&T isn't 4G quite yet either. They are still using the GSM standard still, even with the iPhone 4.