Not quite as simple as business vs. leisure, but I agree that the only reason they'd chose Dec10/Jan10 not Dec10/Dec09 is to make the stats look more impressive.
Then that's really odd, the way any business would normally review a year's performance is to compare December/December, because that's the best way to get a decent comparison without being influenced by factors such as "Our traffic is usually down in Dec." Same thing for other time periods - if you want to see how good traffic was over a weekend, you don't compare Sat/Sun to Thur/Fri, you compare Sat/Sun to the previous week's Sat/Sun.
Our traffic is usually down in Dec.
Oddly, I've found that to be the case every year, across a range of non-business for-leisure websites.
I wonder if they avoided a December 2009 to December 2010 comparison on purpose (or if they preferred the Jan-vs-Dec one to get a better growth).