Andreas -
Hi and thanks.
The alternative that I chose for ToonTalk is that when a user doesn't care about the relationship of real time and simulation time then they can do something similar to eToys and just change things by a constant on each cycle. But when they do care they can move forward a constant times the duration of the most recent cycle. This makes real time and simulation time identical at the cost of a bit more complex programming idiom. (Actually in the case of speed there is a built-in that does this for you, but the problem then returns if you want to program a constant acceleration.)
I lean towards the idea of encouraging kids to explicitly program to account for the passage of real time but my colleagues in WebLabs are sceptical and rather hide this complexity. Maybe explicitly relating real time and simulation time is a good learning oppurtunity for kids.
Best,
-ken kahn