There's only one U.S. Internet company spending big on acquisitions this year, and it's not who you'd think.
The online travel agent followed up its $1.6 billion purchase of Orbitz in September with plans this week to buy vacation rental site HomeAway for $3.9 billion in cash and stock. Earlier this year, Expedia bought Travelocity for $280 million.
Of the 10 most valuable publicly traded U.S consumer Web companies, LinkedIn is the only other to do even a single billion-dollar deal this year. The professional networking site spent $1.5 billion on Lynda.com.
Expedia Chief Financial Officer Mark Okerstrom said the recent activity is the product of a massive technology overhaul the company undertook in recent years to create a more unified platform that takes advantage of modern data and analytics tools. That work has made it possible for the company to plug in other systems.
"It's the strategic decisions we've made and the progress we've seen as a result," Okerstrom said in an interview. "We're set up to take advantage of opportunities, but we didn't set out to start a grand roll-up strategy."
The company also has the benefit of a surging stock price. Expedia shares have jumped 65 percent this year, closing Thursday at $137.31 (they were down a bit Friday morning). Three-quarters of the HomeAway deal is in stock, with $1 billion paid in cash. It's expected to close in the first quarter of 2016.
With rival Priceline Group building up its vacation rental inventory and Airbnb aggressively expanding across the globe, acquiring HomeAway was the best way for Expedia to play in the red-hot home rental market. Evercore ISI estimated in April that the addressable market is $100 billion in terms of annual bookings, with the majority of it still "up for grabs."
HomeAway, whose properties include VRBO and VacationRentals.com, drives $15 billion a year in bookings and is on pace to generate about $500 million in revenue in 2015.
Read MoreAirbnb scores win in California
"These acquisitions are consistent with our expectation that Expedia will engage in M&A to support revenue growth in a highly competitive and consolidating online travel space," wrote Stephen Sohn, a credit analyst at Moody's Investors Service, in a report.
Just how silent has the rest of the Internet sector been?
Facebook hasn't had a $1 billion deal since buying virtual reality company Oculus for $2 billion in June 2014 and the $19 billion purchase of WhatsApp four months later. Both were announced in the first quarter of last year.
Google's last 10-figure deal was the $3.2 billion purchase of smart thermostat maker Nest in February 2014. Priceline acquired OpenTable in July of that year for $2.6 billion, and two months later Amazon.com spent close to $1 billion on video game-streaming site Twitch.
Whether prices for potential targets are too high or the big companies are all busy absorbing teams and products from prior acquisitions, it's been Expedia grabbing the headlines.
The slowdown is certainly not the result of higher capital costs. Expedia said it will consider tapping the debt markets for at least part of the $1 billion in cash it's paying in the HomeAway deal. Expedia had $1.5 billion in cash and equivalents at the end of the third quarter.
"We'll be opportunistic," Okerstrom said. "We'll see how the transaction progresses and how the debt capital markets shape up."