XBOX 360 and the imac 24

No. Only the 27" iMac can be used as a monitor (with an adapter for most devices).

 

Really? Is there a specific reason for this? Is this only saved for the pricier models or something? If so, is there a possibility that the lower end imacs receive this ability later on?

 

Because the 24' iMacs display output can't be used as an input. Simple as that.

Not only because of what I said above, but because the 27' iMac is a newer model, therefor it has newer features

 

Because on that machine, the video port is output only.

 

Probably in a future model.

 

Hopefully, they'll include it in the updates in a couple of weeks...