I think it's a matter of catching it at the right time. At 1amp my 30 gets quite warm, but only at certain times. Most of my batteries with the charger inside have done this.
I think the 30 stays cooler @.5amps when hooked up to PC. If you're worried that's it's on the verge of venting, that'd happen Real quick and be almost untouchable.
If you're uncomfortable with the heat, just use a .5amp USB Hub. Still charges reasonably quick.