In my opinion they, the grenades, are there for show and to add detail to the models. TFC was just a spam-fest of grenades and I would hope that would not be brought into TF2 gameplay. The demoman is all about grenades, so they should just keep them all with him.

If they brought back grenades, wouldn't that defeat half the purpose of demoman? Also, TFC was known for grenade spamming (I loved TFC, but grenade spam was a no no for me), TF2 nade would just be another TFC fail.

The Demo fires those nades he has on his chest, they might look different, but that's because they are in a kind of holster. For soldier I'll think it MIGHT come as an unlock to help him take out things around corners

There are already grenades in the game, I don't get why people don't class projectile explosives as grenades, they're the same damn thing!

Demoman should be the only class with grenades, but that's just my opinion made out of logic and hatred of other classes.

What's the point of having a class made for demolishing enemy buildings when any class could do it?

They wont, In the commentary they remarked as one of the game play problems of tf. They tried to balance them into tf2 but ultimately failed. The grenades on the pyro, demo and soldier are all that remains of the grenades. Then again if the Jarate has an area of effect it would in a way be considered a grenade...