files without write permissions

Is there some reason (maybe I'm just missing something fundamental here)
why:

bk sfiles -x | bk new -

wouldnt work for files that have no write permissions set ?

I get "cant get write lock" errors for those files, although
I'd like to keep them revisioned "unwritable" anyway, is
there an optoin to bk new that I'm missing ?

I see there is a "-M" option to set the mode, but when I check
it out, will it remain "unwritable" ?

cheers,
                -Tristan