I really don't think they are similar. But you are right, it depends on what you want to do as to which one to use.
Cobranet based networks make good use of cable bandwidth but have a very large propogation delay. If you are doing multiple 'hops' you can lose tens of milliseconds. This is why Cobranet is never used for broadcast as the sound is out of sync with the pictures!
BSS Soundweb makes appalling use of bandwidth in comparison but its propogation delay is microseconds. Needing multiple channels in Soundweb needs more cabling - until the new version comes out...
I would not advise using an existing lan and running Cobranet down it. You should have a dedicated lan for audio without the possibility of other data getting in the way. Peak Audio do not recommend other data on the network. Even Media Matrix has seperate data ports to get you to run data an alternative route.
Its good that Cobranet is a 'standard'. However I have been in situations where I have tried to connect two manufacturers equipment together and neither will guarantee that it will work. In reality it probably will, but if it doesn't, you are on your own. Neither manufacturer will support it so it being an open standard is less compelling until the Cobranet licencees sort out this support issue.
I agree the way multiple Audia devices appear as one whole system is neat, but this carries the risk of phasing problems in your design. If audio is sent from one DSP and back again, with the propogation delay this entails, this can cause problems. It also makes it difficult to switch off bits of your system as you might accidently switch off audio in areas you wanted to retain.
This whole category of equipment is changing all the time. All of them currently have severe flaws. Most of these flaws will dissappear when they all have massively faster networks and much more DSP.
