Currently these are our most used tags. That is something I would expect to remain constant. Any question that is tagged "nlhe" could also be tagged "texas holdem" however there is the potential for "texas holdem" to be used on pot-limit and limit questions as well as nlhe questions. In that line of thinking, it makes sense for it to stand on it's own.
The only reason I question this, however, is that by having the nlhe tag separate, we are already seeing some questions with only "nlhe" and others with only "texas holdem". That leads to making it hard to find all questions on the topic.