This really isn't that big of a deal, but you see it happen over and over again - an Editor-in-Chief or an editor or a creator or whoever make some guarantee and odds are the guarantee is not going to hold - so why make the guarantee?
Why not just "we don't plan on doing that"?
Joe Quesada, after House of M/Decimation (courtesy of Newsarama)-
Editorially, Quesada added, there is now a mandate that no new mutants can be created wholesale - only five or six new mutant-based characters that were already in the pipeline will be seen. And that the ones going away won't be coming back...
"As long as I'm here as Editor in Chief, they're not coming back,"
Since that statement, Polaris, Professor X, Magneto and Quicksilver have all regained their powers, through various and sundry methods.
So, "as long as I'm here, only the not so popular mutants will not be coming back"?
Like I said above, it's not a big deal, and I understand that it is totally driven by fan expectations - if you DON'T say something definitive, then they take that as definitive the OTHER way - "If you won't say that the mutants will not regain their powers, then that means that they definitely WILL regain their powers!" So I am not really blaming editorial for this state of affairs, but it is still pretty silly, and I'd prefer it be avoided if possible.