Whatsapp sold for 18 billion due to their user numbers, not their tech. Anyone can create what that have
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If that's the case, then 18 billion seems way overboard for something "anyone can create". What's certain though, is that at this point, nobody can create what Geoff Taylor has spent 30 years creating. If market valuation can be reduced to mere users, one should get out the commodity pricing manual, because that's essentially the model you are invoking.