Doesn't a Texas senator need 50 other senators to back him so that any meaningful arm-twisting legislation that would only benefit the state of Texas could be passed? Or a New York senator? Or a California senator? How does that get done? By making deals with one another. The senate was specifically put in place in order to PREVENT large states like New York, California, and Texas from bullying smaller states like Iowa - it gives all states an equal voice. And considering Grassley has been there a very long time, not only does his presence demand the respect from the rest of the senate, but he probably has collected hundreds of IOUs that perhaps has come time to cash in...
That's great, I'm assuming you realize that for anything to happen he'd have to get the same bill passed in the House as well.
The problem with your argument is that there really isn't that many states that are hurt by expansion, a dozen or so that won't be helped or harmed, and a whole bunch that would actually be helped.