What's funny is that searching for "cute framework fixed timestep" in Google points to this Hacker News thread as the first result. What I would have wanted to find is this page:
If you divorce the game's time-step from your math it isn't too much of an issue. You just need to keep track of the time-delta so you have it for your calculations.
Assuming the timestep refers to the parts of code dealing with game logic updates, such as physics or motion, variable-sized steps tend to cause nasty issues. Collision detection is an example, where variability is undesired.
It really isn't.