Your use of the term "network effects" is a touch loose. Network effects refer to a situation where the product becomes more valuable with more users. This is not the same as simply having a large customer base. Probably the better way to say it: "Microsoft and Facebook both gained advantages because their customers had high switching costs."

FB users have high switching costs in terms of opportunity costs (by leaving FB they forego value) and those opportunities costs are large mostly because of network effects.

In the case of Microsoft, you say "network effects of their enterprise sales channel," when you really mean Microsoft had a large customer base to which they could quickly and easily deploy new products. The fact that one business had a sales agreement with Microsoft didn't necessarily increase the value of a sales agreement with Microsoft for a different business. (Maybe there are some network effects there, but they aren't obvious and I'm fairly sure you aren't talking about them.)

I think Microsoft did (and still does) benefit from network effects in a different way, related to collaboration: the more people who can open and use an excel spreadsheet, the more valuable it is to learn and use excel.