SOAP is simply a well-documented wire protocol. While it appears that Microsoft is getting behind SOAP and will probably provide some form of implementation in future, this doesn't mean that other vendors can't also do the same. The Perl implementation of SOAP is a great example - it's not tied to COM or Windows in any way, and can be used on any platform where a modern version of Perl is available. SOAP is not about tying anyone to a particular platform. It's about providing a reasonable way to communicate over the Internet that is really easy to implement on any platform.
SOAP says nothing about language bindings, rather it is simply a wire protocol.
The basic Perl implementation, for instance, took about half a month for one person to implement. This simplicity is one of the things that makes SOAP attractive. SOAP offers several benefits over a proprietary XML vocabulary. SOAP is an open standard with a growing body of developers and vendors supporting it. As more vendors offer SOAP products and services, the advantages of using SOAP will become more pronounced.