A router is in a whole different neighborhood than a switch or hub. Switches an d hubs provide basically the same service in different ways in that they connect together computers on the same LAN. They're basically cabling extensions. But a router actually transmits data from one LAN to another. It receives data that's not destined for it specifically and determines if the data needs to be passed on and, if so, to which network. To confuse issues more, many, if not most, of these home DSL/Cable routers also have an integrated hub or switch on the home side.

But a router itself cannot provide greater speed internal to a LAN. It's really just another computer on the LAN. It can only provide faster or more access to networks beyond the LAN.

So not knowing exactly how your network was set up before or now or knowing if your router has a hub built into it, it's hard to say why it might work better. I doubt that most of the router-built-in hubs are switching hubs, so it's unlikely to be something that a switch would improve. Maybe your network went from 10Mbps to 100Mbps. It's easily conceivable that your NICs didn't autonegotiate to 100Mbps when just using the crossover cable.