Simply put...it is different because it is an exploit. I am sympathetic to people losing something that they found enjoyable but not everyone used it to bring in harmless vehicles. You can not seriously fault a company, who gets bashed daily for how broken and bug ridden their game is, for fixing a bug/ glitch/ exploit just because it happens to be one you enjoy using.
It looks like the firetruck no longer spraying water was a mistake.
To each their own. There were a lot of people who loved bringing in cars from singleplayer. Besides the duping threads, this hit the MODified crew hard. They can't do what they liked to do anymore. It wasn't hurting anyone, so how was it any different than enjoying races?
If fixing things that are broken results in removing all your fun you are finding your fun in all the wrong places.
I didn't use it personally, but I do feel bad for the many members who are affected by this. In the Spring Update newswire post, Rockstar did say that fun harmless glitches would be left.
In general, we are open to keeping unintended glitches in the game if players enjoy them and they arent causing any negative impact to gameplay or fairness in any way.
They also took away the armored car glitch. That one I will personally miss. We need less things taken out and more things added. And the bugs that are addressed should be the ones that are game breaking, like the console freezes. I'm not a cash card conspiracy guy, but you've got to admit that anything that can make extra cash or allow free cars gets a high priority.