Barack and Michelle Obama are both pretty classy people, and both are (as far as I can tell) pretty stylish. Now, being a guy who would rather wear sweater vests, tweed, and a driver's cap (at the tender age of 22, no less!), I don't know much about fashion. Oscar de la Renta, Gucci, Fabrege (I don't think that's a stylist)...it just doesn't mean anything.
However, I do know something about old-school style. President Obama's people apparently don't.
The President committed a major fashion faux pas when he showed up to the inaugural balls in *gasp* a white bowtie without a tailcoat (see below; Michelle created a tiny stir by wearing white in winter, which is a less well-defined no-no).
To be sure, they both looked very good. However, the President needs to learn a few rules of society. He may know them and have just jumbled them up a bit, since he's done the full formalwear correctly in the past:
Here are the simple rules for the average layman. First, and most importantly, a guest never overdresses for the occasion. The host always sets the standard. Most balls nowadays are 'informal' (which, in society lingo, means 'black tie'). When they are informal, it is rude to show up in full formal attire. That begs the second question. What is full formal attire? Traditionally, for men, full formalwear entails a wing-collared shirt, a tailcoat with notched lapels, a white pique tie and vest (vest must be low-cut, tuxedo style; non of this 'prom' junk that buttons up to your chest), and pants with two thin satin stripes up each leg. A pocket square is a nice addition, as is a carnation or other white flower in the lapel. White dress gloves are also a nice touch.
It is, of course, not that big of a deal. Styles change, and a president (especially one with as much of a pop-culture following as Obama) can play a big part in changing that style.