History first: Presidents do this. Bush did it. Clinton did it. The more the Senate becomes a place where minorities block appointments all over the place, the more Presidents are going to rely on more annoying tacics.
President Bill Clinton made 139 recess appointments during his two terms in office, and President George W. Bush made more than 170, according to the Congressional Research Service.
Politics: Um, the Republicans in the Senate have done little to demonstrate to Obama that seeking their goodwill is desirable or a worthwhile endeavor. Thus far, they vote no as a bloc. They don't bargain. So, why should he treat them like anything else but a speed bump? Bipartisanship takes two sides, and the party of No cannot have it both ways.
Perhaps they expected differently since Obama was a Senator. Perhaps Obama decided to stick it in and twist it a big with the appointment of Craig Becker, the union lawyer for the National Labor Relations Board. If Obama is feeling stronger due to the victory, and using his new leverage, then the Republicans again can blame themselves for not giving him any incentive for playing nicely.