He adds that with little sign that they will properly re-write their apps for WAN use - "although there's always some optimisation going on" - there's still plenty of room for companies such as Riverbed to differentiate themselves according to how they optimise network traffic.
Lewis foresees this technology becoming "invisible" in the long run - Riverbed's software can already be deployed in visible or invisible mode, depending on whether or not you want the users to be able to see it's there and check what it's doing.
But he says that it will still be within a boundary, so a Riverbed client will only co-operate with a Riverbed head-end appliance.
Shifting up a layer
Of course, even if Microsoft removes the need for some of that base technology - for Windows users, at least - there will still be a need for WAN acceleration appliances in the data centre, because of the sheer volumes of data going in and out.
Silver Peak Systems has said that is why it will never do a PC client, for example. Its target is the backup and replication links between data centres and the connections out to branch offices, not those to roaming laptops - and marketing VP Craig Stouffer argues that this market is plenty big enough.
Blue Coat's King agrees that appliances will still be more network-efficient once you have multiple users in a remote site. That's because if they work for the same organisation, it's likely they will be using the same files and applications over the WAN, so having a box means they can share its caching capabilities.
"Even for two users it's more efficient to have an appliance, though once you figure in the cost of the box, it becomes cost-efficient at around five users," he explains.
But he acknowledges too that with more and more users going mobile, PC client software is no longer a nice-to-have - it is now a must-have.
"We're already winning deals and swapping out other suppliers because we have a client," he says. "I think that by the end of this year, if you claim to be a player in WAN optimisation then if you don't have a PC client you're done."