There's change for improvement, change for budgetary reasons and change for the sake of change. If Wheeljack, Jetfire, Bumblebee and Ironhide suddenly became a combiner and formed a giant robot named Wheelie, you'd be cheering all over that?
No, I wouldn't. There are somethings that are iconic in comic books and continuities. I can understand why Bumblebee wasn't a VW but they still should have had him as a small car.
Would you like it if they changed Superman's origin? Or costume around? Or how about Batman's origin? Let's say his parents weren't killed by a thief? Or let's say Wolverine wasn't a Canadian...How would you deal with those changes?
I for one wouldn't care too much because I understand the industry is a business and there are certain changes that must be made in films due to budget. It also has to be a story the mass public can relate too in a short period of time. Even books made into movies get altered for this reason.
When you understand how a studio & the film making business works, you might come to understand how all this complaining is silly.
No movie is just made for it's fan audience, they're made for the mass pubilc all over the world to relate too.