Honestly, because even though it's a yearly trend to say how bad the Skins are, if we look over the last 5 or 10 years they've been no better or worse than average (made the playoffs a few times, have had top 5 defenses, have had a dominant RB in Portis for a while, etc.). If you add arguably the best DT in the NFL to a team with a top 5 defense that just didn't seem to get enough pressure and turnovers, that could make an average team good... then you draft the left tackle of the future and add a great leader in McNabb and you may have a contender in a couple of years.
Now the reality is they need A LOT of depth at many positions, especially oline, Big Al's off the field impact needed to be considered, and today's NFL isn't one that likes to wait a couple of years... so yes, it was definitely a bad signing. I just wanted to give a perspective (though shortsighted as stated) where it made some sense.
OT but the Nats example could have the same logic. Add a solid vet that can be a #3 starter and expect healthy years from Strasburg, Zimmerman and Hill and you've got a decent starting rotation... and that's THIS year. It can be built on moving forward. Bring in Harper and now Werth and even though they lose Dunn, the lineup still has a bit of bite too.
Like with Big Al, I agree with you... that's way too much money for someone like Werth, and things never go perfectly so they'll still have some issues that will keep them down unless other moves are made, but I can see how someone processed the deal in their head.