I don't think he's saying "don't sell hosted Exchange or SharePoint", he's saying "don't host the services youself". Office 365 is cheap. It's a professional service, it's spread across multiple locations, it's got big fat pipes, automated failover, redundant power sources, proper cooling, backup systems etc etc. Sure, anyone can put Exchange on a little old server in the corner and sell hosted Exchange for cheaper. It's all good until the power goes out to your building, or until the machine needs a new motherboard, or you realise the backups you've been religiously taking don't want to restore.
It's not that you can't do it, it's that it takes a lot of resources to do it properly. And if you don't do it properly you're gambling your companies reputation.
Remember too, he didn't say "don't ever do this". He said "think carefully before doing it".
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