The 4 cylinder e89's never had hill assist. I know this as I had one when they did the deal with about £8k off. I got mine in 2012 - all the literature - brochures, website etc said it was a "standard" feature, but when the cars started arriving to customers we found out it wasn't. It was only then available on the 6 cylinder cars. I think it was available on the previous models, sdrive23 etc...
BMW would just say "did you clarify with your salesman if the car had that feature" and I would say "no, cos its a standard feature...I didn't clarify other standard features, ie windows!". They then tried to say that the brochures showed things that were only in certain countries....they didn't like it when we pointed out it was also on the UK website when speccing a UK car!
Took them a while to remove it from the website.
My salesman didn't even know - I phoned him up just before my car was delivered and he had to go out and try one...he thought it did, and was surprised it didn't.
Some people got about £300 compensation. Was a real c0ck up, because as we know, it was a technology that had been around a while.
My main moan was that because the ebrake has a delay, it was hard to get the biting point. When I got mine, I went to the steepest (quiet) hill I could find and just practiced moving off...after about 5 attempts I had it where I could pull off smoothly, not jerking etc.
Unfortunately I only had that car 2 years. Now I've got another!