Clearly, it was changed to leave the door open for sequels, and to do a product placement for the new truck Statham drives off in at the end.
Ultimately, business decisions made my business people at whichever corporation owned the rights.

His whole character right through the movie is far different from Bronson's portrayal, so I think he'd probably be happy with the way things ended.

I guess you would - and if you had two insiders talking you'd probably end up with two (or more) different versions - and they'd possibly both be telling the truth as they remember it. But I suspect Stratham is actually a good actor and I wonder if he'd have liked to follow the original story line more closely?
I have always depended on the kindness of Strangers - and the bastards let me down!

I love this movie and I think it's one of Statham's best, but I can't answer your question. You'd have to have real insider knowledge to know what went on back then, wouldn't you?