The GP isn't arguing that Dell/HP are hurting because they lost their biggest customers. It argues that they're at risk of losing many customers in the future, because enterprise IT departments will emulate Facebook and Google.
If that is his argument, then I think it's wrong. Small and medium business will never do that for sure. They don't have the knowledge, resources or anything. The ROI is nonexistent for them.
Even for big corporation, what would be a good number of servers for them to reach a critical mass where it is worth keeping all those HW engineers and increased support staff? They want to sign a contract, get regular supported servers, with warranty, etc, and focus on their core business. They get it from the regular folks of HP, Dell, IBM, etc.
Of course there are exceptions but are they numerous enough to say Dell and HP are doomed? I hardly think so. Corporations in HPC market might take a stab at creating something like this. The folks running app/DB/web/whatnot servers for ERP, financial, etc applications?
