What specs are you talking about specifically? It doesn't look like a server at all.
The specifications are on a par with low-end consumer-grade NAS products, and it has a USB 3 port, but nothing on the site says anything about providing storage or other services, except for router-type and supporting configuration services (I suppose "keep an eye on your network" is a bit of an extra).
"Plenty of room, OnHub has 4GB of storage space, so there’s plenty of room for auto-updates and the latest software features" is hardly selling a server. All it claims to be is a fancy router.
The detailed specs page shows a 1.4 GHz Dual Core processor and a 1GB of DDR3 RAM. Thats a little ridiculous for a router
At some point you need a general purpose CPU to run everything and it's not hard to just throw an ARM SoC at it which is going to be in the 1-1.5ghz range and dual core because that's just what low-end is now.
Agreed, the specs between the WRT1900AC and the OnHub are strikingly similar. Even the advertised smart features.
The RAM is about 4x what other routers are packing but the cost difference between a 1Gbit chip and 4Gbit chip is a few dollars. Prices have been plummeting this year and 8Gbit chips replaced 4Gbit as the new hotness. Not to mention DDR4 rolling out so there might just be dumping going on that makes adding 1GB of RAM a non issue.