Very good point Blastoff however in this specific case I am not referring to a country operating under FAA rules per se. That did get me thinking.
In Australia for example under sub regulation 308 and 252 the ERJ 170/190 is exempted from requirement to carry a life raft in overwater flights 60 minutes or 400nm from land.
Another interesting point arises that in the country which I am thinking of the route described may fall outside the Part 121 definition of extended overwater flight, since it is not an ETOPS flight, but rather is within the 90 minute rule and only "extended" operations are required to be certified for ditching.
The other point is that with a life raft in the cabin (as Qantas do on their B733 ETOPS flights) one loses a row of seats on the ERJ-135LR and thus the aircraft becomes subject to Part 125. There is no ditching requirement for Part 125, nor can Part 125 aircraft be certified for ditching anyway.
In any case given the distances here it is doubtful the aircraft could be operated with more than 30 pax.
In terms of decompression we're also talking about 530nm from any given diversion field. What's the fuel flow increase at 10,000 feet ?