The stunning news that Apple bought social search engine, Topsy, for more than $200M has many scratching their heads. Why would Apple want social data, and why would they pay so much for it?

There has been a lot of speculation about the reasons for this acquisition — ranging from making Siri better, to making the App Store smarter, to acquiring big data expertise to develop insights on the Apple firehose.

But I think the reason may be something else altogether: Personalization.

If you want to build the next-generation of smart personalized mobile apps and services, you need a way to know what your users are interested in.

Well, what about analyzing everything they’ve ever Tweeted? That’s a pretty good shortcut.

I know from experience how well this approach can work. Analyzing consumer Tweets provides a surprisingly good window into the interests, relationships and affinities of consumers and brands.

(Disclosure: My company, Bottlenose, which focuses on trend intelligence from social firehose data, has done quite a bit of work on deriving user interest profiles from Twitter timelines, and among our 28 pending patents we have a number of applications around this.)

The Topsy deal is not about search. If Apple wanted to build a social search engine, then only searching Twitter history would not be a winning strategy. To win at social search a service has to be real-time, and should encompass many other social outlets — not just Twitter.

Topsy is much more focused on historical data than the present moment, and they only cover Twitter data. The Twitter-centrism and historical focus of Topsy are weaknesses, unless social search is not really the goal.

Topsy’s real strength is that they have indexed every Tweet in Twitter’s history. The only other known company that has done that is Twitter. This history is a goldmine for personalization. This is what I think Apple really bought.

The next frontier for personalization is contextual awareness. Mobile apps that know more about their present context, and the user, can provide even more relevant and timely suggestions.

But contextual awareness is not merely about knowing the device’s position. It’s about knowing everything about what a user is doing, who they are, and what they might think or want next.

The goal of contextual awareness is to create apps that understand not only where you are located and what you are looking at, but also what you are doing, why you are doing it, who and what is nearby, what your goals are, and what you are likely to think and feel about every person, building, device, object, app, product, advertisement, or bit of information you may encounter.

Google is already ahead of Apple in the contextual awareness game with Google Now and Google Glass. Facebook and Twitter both have huge advantages over Apple in this area as well because of all the data they have, and their large mobile footprints.

If Apple wants to compete in this arena, it needs to shore up it’s own apps and services with a way to understand each user’s present context and interests, and the history of what they have said about every location, product and piece of content they have encountered.

From Siri, to iTunes to the App Store, to Apple Maps to Apple’s alleged next-gen search, augmented reality and TV initiatives — context is king.

With Topsy’s historical Twitter data Apple can not only to make Siri smarter, it can power a whole new generation of smarter contextually-aware Apple apps and services. Apps that listen to, watch, and learn from, what users say and do.

Now all of this assumes that Twitter will just sit back and let Apple beat them to the contextual awareness Holy Grail on their own data. But will they? Apple and Twitter have a close relationship already. But could this new move by Apple change the tone of that relationship? It might. I would be willing to bet Twitter is starting to feel a wee bit claustrophobic right about now.

Twitter cannot tie itself only to Apple; Android matters too. Plus Twitter wants to control its own consumer experiences, and they need contextual awareness too. If Apple leapfrogs Twitter on the contextual awareness front, how long will Twitter continue to supply their full firehose to Apple’s Topsy team?

Twitter certainly has to walk an increasingly fine line with Apple, their $500B market cap frenemy.