airport express to receive wirelss > bridge to wired

[arri]

i'm sorry if the answer is too obvious,
as i would think reading this article:

http://docs.info.apple.com/article.html?artnum=108038


still, i find it very hard to believe that the following scenario is not possoible:

to have the Airport Express connect to an existing wireless network, and have it simply bridge this network to it's ethernet-port.

it just seems stupid why it shouldn't be capabe of doing this,
all components (hard-/software-wise) are there.

is there not some 'unsupported' backdoor?