Why are global variables *non-deletable* properties of the global object?

[Chris Pine]

Brendan Eich wrote:
> Works correctly (true, false, 43) in Firefox 3 (try it, you'll like  
> it!).
> 
> That looks like a Firefox 2 bug, probably to do with "inner and outer  
> windows". Don't ask (security requirement of the DOM level 0,  
> implemented similarly in IE and Firefox, IIRC coming soon to Webkit,  
> very probably in Opera; but thanks for pointing this out!).

(true, false, 43) in Opera 9.5

Chris