How? They already have the data and plumbing, all they need is a GUI. I don't think Google would go for a Hipmunk-style GUI, they'd just build something search-based you could see in your results.
It shows Google wants to be in this space and is willing to buy into it. I don't know that Google will specifically go for Hipmunk, but when any major corporation starts buying into a market, they tend to make more than one acquisition, and it's often the partners of the big companies they acquire first. I'm pretty certain they'll make a couple more strategic acquisitions in the airline/travel space, and Hipmunk is one of the more interesting partners of ITA, since they're new enough to probably be cheap (single or double digit millions, if Steve were looking to be acquired), and all the original team is still in place, no one has cashed out. Hipmunk is also one of the most interesting teams in the space.
Further, if I were doing a talent acquisition, I can't think of many people I'd want more than the reddit team, and Hipmunk is currently pretty much made up of the early reddit team. Of course, Steve is already rich (by some definition of rich), so probably isn't desperate to sell for merely "talent acquisition" money, but Google can afford to stretch the meaning of talent acquisition, and have done so in the past to get really interesting people.
Also, saying "all they need is a GUI" is vastly underrating the importance of the GUI. I can imagine an Android app with a Hipmunk style UI being really powerful. Sometimes you want to find the perfect balance of price and schedule, and sometimes you want to do that while in the middle of a meeting or in the cab on your way to your hotel so you know when you're flying again, or whatever.
And, to get specific about YC-related acquisitions, Google docs had a spreadsheet when they acquired Zenter. All they needed was a GUI, but they acquired a two-man company that had a few tens of thousands of lines of code. Probably a talent acquisition (and a smart one, since Robby and Wayne are awesome), but nonetheless, an acquisition.
Anyway, I agree that Google will definitely be building this into the search user interface. But, when Google moves into an area they don't just do the search interface. Maps has loads of entry-points into it, including non-search oriented use cases, and Google made several acquisitions and developed a bunch of stuff internally to make Maps happen.
It could also be viewed as epic validation that the ideas are gold. I most certainly believe Hipmunk can compete against Google; the team is completely awesome and they're far more nimble and agile. Although Google does have an unbeatable vision of Maps I'd imagine...there's no real reason you shouldn't be able to get bus times and airplane times in the same place. And perhaps if you could then pay for the bus and the plane using your Android NFC...
They could probably spin new features faster than Google. For example, every service I've seen requires a departure date and return date. In my head, I thinking, "I don't know - sometime this summer." I'd like to be able to pick a destination, the number of days, and have it tell me when I should go on vacation to get the cheapest fares.
