The only thing that would make that investment irrelevant would be the existence (not announcement of a desire to create) of a far larger open network. If Skype in fact has tens of millions of ordinary users who routinely make telephone calls through it, a "far larger" network just isn't likely.
Basically it's the walled garden thing again. Having the Internet, nobody cared that they missed out on MSN because MSN was small and content poor and the Internet was already huge and had everything you could want. But suppose MSN had included exclusive movie streaming back in the mid-1990s. Suddenly nobody wants the Internet, except as a freebie thrown in when you pay for MSN from Microsoft.
For telephony the "content" is people (or to a small and reducing extent, businesses) you want to call. Skype users are walled off, you can't call them unless you're a Skype user. If 1% of the people you want to call are Skype users, they're the annoying holdouts and you tell them they should switch. But if 50% of people you want to call use Skype, you switch to Skype too so that you can call them.