Well, they are. It is worth mentioning. I spend so much of the time in my games with my marines inside their Rhinos trying to protect them and move them. I often forget just how tough and durable they really are until I am forced to remember.
Take this last game which I played as an example. I had 4 of my 5 Rhinos popped, forcing the marines outside their protective shell. One Rhino was the Death Company Rhino, and they are not exactly regular marines, so we will not consider them. However, the other three destroyed rhinos forced out one Tactical Squad and 2 Assault Squads.
The Tactical Squad was destroyed, but the Assault Squads (5 man) lasted until the end of the game. One these Assault Squads claimed a game winning objective.
I just felt like stating the obvious here (because if you are like me, you need to be reminded sometimes). We are not talking about Imperial Guardsmen. These are Space Marines. They are durable, tough, and capable warriors. They are able to accomplish their mission and bring death to the enemies of the emperor.
They still have that high stat line, as far as standard troopers are concerned. They still have the best individual equipment that the empire can offer. I have in mind here Power Armor and the Holy Bolter, or Bolt Pistol and Chainsword.
There are many table-top applications to this truth. Here is one: Park that Rhino on top of the objective. Your Tactical (or Assault for Blood Angels) Squad can claim the objective from inside. Your opponent must destroy the Rhino, and we all know the increased difficulty of destroying vehicles in 5th edition. After your opponent destroys the Rhino, he still has a unit of durable, tough, and nasty Space Marines to kill.