I feel it is not so much "better sphincter control when the bladder is full" as much as that when the bladder is holding something, generally the unconsciously controlled valve on the bladder is closed and only needs to be supported by your kegel activity.
I don't think it is so much "the bladder sends automatic signal direct to spincter?" as your kegel work tightening the sphincter (the sphincter that you consciously create) eventually learns to communicate with the smooth muscle bladder valve to open and close. The bladder after surgery has been stretched and this not-consciously-controlled valve (like your heartbeat is not consciously controlled) often just stays open for awhile until it becomes accustomed to its new "stretch" position - and importance!
If you have some time, possibly read my thread on "Zen and the art of.... continence" (currently on page one). For those of us that do not achieve immediate continence, the "elevator kegels" discussed there seem especially helpful.
I also STRONGLY recommend that you look at the direct links on Bluebirds "Helpful Hints" thread and read about doing kegels on the stairmaster! Bluebird is famous for helping all of us here in this community find what we need - and to use our talents and knowledge to join in helping others where we can.
I myself have regained most continence (I drip a little each day - as I unload trucks....) as I approach the 4 month-post-surgery mark. Now I look toward E.D. (erectile dysfunction) rehabilitation. While it may be a little soon for you to work on this area, I heartily recommend you follow all of the threads on E.D. as well. A few weeks after surgery, it's all about keeping the circulation going to the nerves.
Social comparison can lead to unrealistic expectations about how long it takes an individual to heal. Physicians are not only very busy - I feel they also have to be "oh-so-careful" what they say - or even what they appear to agree to if we make a statement in front of them. They know that we must stay positive about our futures. Hope for the best but don't lose your joy if some healing process takes a little longer for you than it does for another.
Your new friends here can each share their stories! We are all healing. Be patient. You will regain continence. Stay with us!