Seven layers are a procrustean bed, at best. The model might be useful as a starting point, but really all it means is "good design uses layers." When you start discussing actual networking implementations, trying to fit a what you're doing into "where exactly this fits in the ISO model, and it's wrong if it doesn't fit" is a bad way to think.
Devices that mix layers can do pretty interesting work, too (e.g., inspection of packets for security purposes, smart buffering for controlling host load, etc.). So the "every layer only talks to the layers immediately above and below" is kind of suspect, at least as dogma. There are probably other examples in very high bandwidth systems where you want to skip layers for performance reasons.
Although I'm not really sympathetic to the OSI model, it did get some things right. For instance, witness how almost every TCP/IP protocol has to roll out its own session layer for authentication purposes...
