Probably just me not explaining myself very well on this. By skinable I mean able to be to skinned rather than requiring one in the first place (I'm dev so language slightly different).

Allowing skins to be applied over a stock look and feel I believe offers a great end user experience. If we can combine that with intelligent control associations (keep associated controls together) and allow configurable UI widgets then everyone is happy: UI becomes just another configuration dataset for the developer.