I really don't know what Google thinks , but i suppose such a lot of advertising revenue is generated in the travel and tourism area that Google want's to keep it's toe in the water , so to speak on continuing to capture as much related content as it can.
But like any other vertical , they won't control it ( my guess ), but they can strongly influence how it evolves. My sense is that there will come a day soon , when SE / Travel search is a lot less dominated by Google and depending on which other verticals you are in, other applications and networking systems may well become more dominant.
Flavour of the month is Facebook at the moment. Who needs Ruba / Google with good creative interactivity within FB and others ( I'm just challenging thoughts here )
Telecoms is another such vertical that will bounce back, i think. Then where will content relationships such as Ruba sit.
The threats to Google keep mounting and it will just reach a threshold ( like Microsoft ) and stick to it's core.