Actually a lot of the history we're seeing unfold is just a recapitulation of what happened the first time(s) around.
When mainframes moved from research and accounting back rooms into the enterprise and then the "multiprise" they also faced interoperability issues over wide area networks. In IBM's corner of the world this is where SNA came from (and came in). Minis faced the same issues later on, resulting in efforts such as Tuxedo - but much of what began in the mini world (including CORBA) got run over by the truck of the microcomputer wave.
Now we're seeing "smaller scale" microprocessor based platforms starting their evolution beyond enterprise as well. This has taken different paths, such as removing the NetBIOS shackles from DCOM a few years back, adding XA to the spectrum of technologies in the J2EE palette, and so on. Growth has occurred in a number of directions.
But the limit to growth toward the "multiprise" has been those old, inherently synchronous methods of coupling the components of distributed systems. In many cases this is a problem within organizations that have multiple "islands of automation" - even when they've consolidated everything into one big server room.
I believe Indigo is just Microsoft's attempt to answer this perceived need in a managed and architected fashion. Lots of us were essentially using "web services" before the name had been coined. It was just done in an ad hoc manner. Some people used TCP sockets, others used HTTP. Some structured the data using HTML tags, later some used XML, and still others just passed "raw text" with their own approach to structuring the data (if only simple CSV-style field/row delimiters). Heck, I worked on projects that did this using bisync and bisync-like protocols in the '70s and '80s before TCP/IP became ubiquitous.
There was actually a fix for DCOM and firewalls before SOAP. DCOM can be run over HTTP using NT4 SP 3 and later. Even MSMQ operated over HTTP beginning with Win XP, though before that you needed at least a TCP connection (port 1801) to go between enterprises.
I don't recall Microsoft claiming that DCOM addressed the issues that Indigo is tackling. They simply didn't acknowledge that the need existed because until recently they hadn't tried playing in that problem space. Until recently they've been like a farm kid on a tractor bound to the family acreage. Who needs rules? Who needs safety equipment? Who needs good brakes? Turn signals? Except now that they want to drive the public roads it becomes a different story.
