There’s niche and then there’s niche. Firmly in the latter camp falls PA2010.com, the 18-month-old site that, as the URL suggests, focuses just on Pennsylvania politics and just on a dozen 2010-cycle races. But even with a niche that narrow — and a web address seemingly destined for obsolescence on Jan. 1 — the site was successful enough for founder Dan Hirschhorn to find a buyer, the Pennsylvania firm Media Bureau. Hirschhorn’s off to Politico, where he’s now an assistant editor.

I spoke with Hirschhorn recently about the site and its sale. Why focus an entire site around just this cycle’s U.S. Senate races, a handful of House races, and the gubernatorial race? “We were covering only 12 races in Pennsylvania, but we were covering those races better than anyone in the country was,” he said. “That’s the value that PA2010 was bringing to its audience — an authoritative voice on a narrow subject area.”

Hirschhorn anchored the site, filing daily, straightforward reports. A handful of contributors and four regular stringers filed posts from around the state. One section of the site runs political press releases; a daily newsletter offers readers a roundup of relevant politics news. The site solicited content from the campaigns, including clips from radio and TV spots.

PA2010 attracts about 30,000 to 40,000 unique visitors monthly, the new owner, Benjamin Barnett, told me. Though relatively small, it’s the kind of readership that appeals to advertisers: influential, wealthy, and largely based in a geographic region. The site was already profitable when Barnett bought it, he said.

Hirschhorn, who graduated from college in 2007, decided to launch PA2010 shortly after his former employer, Observer Media Group, shuttered PolitickerPA in January 2009. PolitickerPA was part of a network of sites that were supposed to grow to 50 across the country. Owner Josh Kushner’s plan deflated when the financial crisis hit. (Only PolitickerNJ still publishes.)

Hirschhorn decided to keep covering races interesting to a big enough group of die-hards to support a site. Just ten days after launch he had proof of concept: After serving in political office as a Republican for 44 years, Sen. Arlen Specter announced he was switching parties. “That’s the kind of news event the site was built for,” Hirschhorn said. “Really, from that moment it was a thrilling roller coaster ride that never stopped.”

I asked the site’s new owner, Barnett, why he’d buy a site branded around 2010 just a few weeks before Election Day. “It was a no-brainer,” he said, explaining that the site’s loyal audience was paramount. “It’s as much about harnessing the energy that’s out there as anything,” he said. Barnett’s purchase of the site wasn’t out of the blue: His media firm had been running PA2010’s social media strategy from a few months after its original launch.

Barnett plans to rebrand the site for 2012 soon after the 2010 cycle ends. He laughed when I asked about the political “homestretch,” saying he’s actually in launch mode: The 2012 cycle starts the morning after election day. (In case you’re wondering, yes, he’s already bought PA2012.com.) Barnett is considering broadening the scope of PA2010 into more local races, but ultimately hopes to target the same politically savvy audience.

“In our opinion, we harnessed this great energy out there,” Barnett said. “Who’s to say there’d be reason for it to stop?”