Its quite a heavy move, brutally portrayed (shot in the stomach by his hypnotised girlfirend) and a natural conclusion to the very cool civil war idea.
Apparently Quesda, JMS, Millar and Wheldon had this whole arc planned out two years ago. (yes, it seems JMS has the Marvel boys thinking in arcs...) so you can't put it down to political headline grabbing. Its just telling a good story, but you can read what you like into it.
I'm a Brit, but I can see how both the left and right in the US read different things into Steve Rogers. As with Civil War, th eleft can see him as the emodiment of all the freedoms the US is in danger of loosing, whilst the right see him as a much needed patriotic figurehead.
Anyhow, no-one dies forever in comics. I expect Frank Castle to become the next Captian America, until Steve R gets brought back...