Given that the currently highest voted answer states it should be allowed and that a diamond mod (other than Jeff I guess) should respond: voila here I am!
I went over to the Stack Exchange Meta list and quote:
So we have several iPhone and other smartphone related SE-sites. Someone explain to me why Super User needs to allow these kind of questions?
The problems I do see is that (currently) there is some fragmentation and you can't be sure what site will gain the most traffic, the best users and most importantly the best answers.
Furthermore, Super User already has higher traffic than these SE-sites, so it would be 'easier' for getting answers on you question there. Personally I'd love to see an API solution that simply let's me browse all SE and trilogy sites for interesting topics through one highly customizable portal.
That way, everyone will have their own version of the SE-sites based on what they personally like. If you're a programmer that doesn't like other topics to cloud his frontpage: good for you, go follow C# on SO alone. But that doesn't mean that there are other people who would like to follow other topics with the same ease.
As has been mentioned in similar discussions: even though someone likes Stack Overflow doesn't mean they instantly like Server Fault or Super User. However, that fact ignores all the users that do! It has been suggested by letting SF/SU question pop up to SO audience could draw a lot of SO's much larger traffic to the other sites. Now I don't want to clutter the Stack Overflow homepage, but do see potential for the API to create a medium here.
This could then also work for Super User and other SE-sites on smartphones, gaming consoles and other peripherals or web-apps.
Stop cluttering Super User with other topics and fix the problem, not the symptoms!