I think what's needed here is a review of the OSI model... at least my interpretation the first 3 layers.
Layer 1 defines specifications for the medium for transmission of electrical signals. Consider these as examples:
* Cat 5 cabling: send/receive wire pairs, twisted once every x unit
* wireless: 10 channels in the 800-800MHz range
Layer 2 defines frames of information to be transmitted over the lower layer. For example, a frame might contain a total of 128 bits. The first 8 bits are the source device, second 8 bits are the destination device, etc. Each protocol will have it's own definition for the way the information is formatted in it's frame.
This is the extent of what 802.15.4 defines. There is no context for a network under 802.15.4. It only defines a medium of transmission and host addressing.
Layer 3 defines networks which allows for the context of routing. This is something that zigbee is trying to do for 802.15.4 by extending the specification. I dont know anything about zigbee, but I would guess that it defines a network space and methods for moving a packet from one network to another.
Here is a link on encapsulation that might help you understand how short/long range frames interact with higher layer routing: http://en.wikipedia.org/wiki/Encapsulation_(networking