You're vastly underestimating the ability of a poor programmer to bring your computer to its knees ;) A tight infinite loop running on any virtual machine will have the same effect.
That's why Javascript interpreters have, blessedly, implemented "Unresponsive Script" warnings that let you kill off those scripts.
Sadly, Adobe hasn't seen fit to offer comparable functionality for dealing with a Flash application that goes berserk. But again, I think that comes down to browsers being in strong competition creating a lot of incentive for them to work hard on efficiency and UX, where Adobe is content to let usability stagnate and bugs fester.
Unresponsive script is different then slow script, flash offers the same unresponsive script warning when a thread gets caught in an infinite loop, and neither environment knows how to deal with a slow script.
Well… Browsers use the same thread for UI updates and JS execution, so every time[1] Javascript is executing your UI is blocked—which means that if your script runs for longer than ~0.2s UI becomes noticeably unresponsive. So IE will decide that your script is unresponsive after 5mil statements, Firefox—after 10 seconds, and Safari after 5. Opera seems not to care
[1] Unless your are using webworkers. Those are executed in separate threads.
Edit: It was incredibly easy to locate this on Google, so I am sure a little research could have worked well for your comment and perhaps saved yourself the possible FUD attribution.
Flash does have an unresponsive script warning. If a script is taking to long to run a box will pop up asking if you want to stop it or let it continue.
