The difference is that Frenzy doesn't have enough fans to bitch
You sire have never spent ANY time in a Transformers forum if you can say this, the whole Rumble vs Frenzy debate is one of the most heated Transformers argument to this day.
Basically it goes like this, Soundwave had 5 smaller cassettes originally, they added more latter but the originals were Rumble, Frenzy, Buzzsaw (the bird that CAME WITH Soundwave BUT NOT featured in the show more than 2 or three episodes, Laser Beak (sold seperately from Soundwave but WAS his sidekick on the show and featured prominatley every single episode., then there was Ravage (the what was it bob cat?)
Anyways it goes something like this, Rumble and Frenzy were twins, the exact same robot mode the difference was ONE was Red and ONE was BLUE. Here is where it gets tricky and WHY it was IMPROTANT to have Frenzy as the name in this movie.
In the cartoon the BLUE robot was referred to as RUMBLE, but the RED robot was called Frenzy (causing most cartoon fans to mix up the names)
The toys AND COMICS switched the names around, the RED robot was RUMBLE and the BLUE robot was Frenzy (but in BOTH cases the BLUE robot was the most used)
So he was the ONE cassette that had the most fans to piss off and pelase at the same time. No matter which name they went with, Soundwave, Frenzy or Rumble, some fans were gonna be pissed.
See the Toys came first so it SHOULD be the standard, but they had a RED Bumble Bee AND a Yellow Bumble Bee toy (there were other mix ups in the series as well, too many to list but worth noting the major ones due to their placement in the new film)
So most fans generally accept the toy colors and names aren't always right, so they side with either the cartoon OR the comics (which had different stories and main characters)
So the comics and pilot of the cartoon both came out close enough to the launch of the toys to cause this mass confusion, depending on which you were exposed to first, toys, cartoon or comics, would determine what name you associated with the RED/BLUE robot cassettes.
So for this movie to settle that Frenzy is the main robot that everyone associated with and was acting as Megatrons right hand man (a role Rumble played in the cartoon and Frenzy played in the comics) so this was likely a way for the film makers to sorta 'settle' the great debate. (even though I take the stance that Rumble is Blue and Frenzy is Red so to me the character in the movies is RUMBLE *NOT* Frenzy despite what the writers may say)
Also I don't get the whole Bumblebee as a sports car hate most people had, in G2 he was a beetle but then turned into a sports car (not an actual Camero but a Camero looking car)
So of all non-beetle alt modes the Camero was the obvious choice, aside from cooperate meddling that is. But a lot of transfans contest the legitimacy of G2 in the first place so why do I even care right?