It surprises me how often I hear this. Many breweries have ONE house yeast.
In order to use a different yeast for bottle conditioning, they would have to keep two yeast strains available, which seems very unlikely to me for many breweries.
I know, it bugs the hell out of me that so many folks repeat this "rote," without even bothering to substantiate it or look at the logic or even the reasons why those (FEW) that do that actually do it.
Very few breweries DON'T use the original strain in their bottles, mostly Belgians disguising their strain, and high grav beers that maybe used a champagne strain to aid in carbonation. Most of the time when we see yeast in the bottles, especially microbreweries like Rogue or even Bell's, it IS the strain.
Most beers have no logical reason to disguise their fermenting strain with another one, so for all intents and purposes you can tend to go with the idea that if it's an american craft beer of moderate gravity that the strain in the bottle IS the fermenting strain. Plus you can usually find online whether or not folks have harvested the yeast for sure. There's a pdf file that lists a ton that I've posted repeatedly here, but you can also type a google phrase like "harvesting yeast from beer X" and you'll see threads about it.