would wd live support asf files?
According to the information on this link Yes !
ASF is just a container format. Many codecs can be packed into it, some of which the WDTV can play others not.
Please read page 154 of the the manual to determine if your files are supported. http://www.wdc.com/wdproducts/library/UM/ENG/4779-705043.pdf
always a catch in this darn device.
Its not a catch of this particular device, its something that happens with any device, even your computer. There are far too many codecs out there and even your computer needs them in order to be able to support a particular media file, otherwise it would not play a non supported file. The difference is that your computer is far easier to enable it to interact with the files than a media player is =P