Difference in FTTC speed between two makes of Router

[#1]

A couple of months ago my PN-supplied Netgear gave up the ghost.  While waiting for a replacement I bought a cheap non-wireless US Robotics 8004 router just to get me back online and to give me a spare for the future.
After setting it up I noticed my FTTC speed was no higher than 20Mbps (it had previously been 32), so I assumed that the power cut that had fried the previous router had also affected the line.  However when the replacement Netgear arrived, I found that my BB speed was indeed 32...using the Netgear.
If I swopped it back for the US Robotics, I only got 20Mbps.
Can anyone shed any light on why this is?  I flashed the US Robotics to the latest firmware, reset to factory defaults and reconfigured it, but to no avail.  It's not really a problem as it was only £15, but I'd like to know why there's such a difference in speed between the two routers.  It seems to be primarily suited as a cable router, and the specifications for the router say max bandwidth 200Mbps so I can't see where the problem is.
- Curious Dave

[#2]

My guess is that the 200Mbps is a typo in the specs and it should really be 20.
Quote from here http://www.tomsguide.com/us/cheap-router-roundup,review-754-9.html

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The USR 8004 from U.S. Robotics is a vanilla router with little in the way of bells and whistles and even less in the way of performance

Not many ( if any! )  home routers would be capable of routing 200Mbps, most would probably be between the 50 and 100 mark.

[#3]

The datasheet for my old netgear router boasts:

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ultra-fast 10/100 switched LAN ports capable of speeds of 200 Mbps

It's the "add together the up and down speed" marketing hype.

[#4]

Strange that they should make the same typo in several places though.  Plus on US Robotics site they explicitly differentiate between 100BASE-TX and 10BASE-T:
Maximum Bandwidth:
Full-duplex: 200 Mbps (for 100BASE-TX), 20 Mbps (for 10BASE-T)
Half-duplex: 100 Mbps (for 100BASE-TX), 10 Mbps (for 10BASE-T)
From here:
http://www.usr-emea.com/products/p-wired-product.asp?prod=net-8004&page=specs&loc=unkg
Plus I think that TomsHardware review is out of date (2006). The router I've got does support UPNP, because whenever I connected anything to wireless, the damn thing kept adding port-forwarding entries until I turned if off!

[#5]

As ejs says, the LAN ports are physically capable of 200Mbps full duplex. However the processing power of the router isn't capable of 'routing' anything like that as throughput between the LAN and WAN side. That's where you are seeing the throttling on the 8004. Throughput between 2 LAN connections may well be a lot higher and possibly approach 200Mbps since it is only going through what is in effect a 4 port switch and won't involve much ( if any ) processing.

[#6]

Ah I see!  So up+down on a 10Mbps full duplex connection equals 20Mbps...10 each way...while up+down on a 100Mbps full duplex equals 200Mbps.  The wonders of creative marketing.
I know what routers do, I just didn't know how they did it.  So it's physical processing power that determines how fast it can route traffic then? 
I have seen one before (I bought one for a friend who had cable about 5 years ago), but obviously that was when cable speeds rarely exceeded 10Mbps, but now we're into the realms of 32/80 Mbps fibre it no longer cuts the mustard!  I did wonder why it was by far the cheapest one in the shop! 
Well it'll do fine whenever I need a temporary spare, or to check that a fault isn't router-based, and £15 isn't a bad price to pay for something that's basically going to live in a drawer 90% of the time.

[#7]

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So it's physical processing power that determines how fast it can route traffic then?

To some extent, yes. When its routing between WAN and LAN then there is a need, at least, to process each packet to translate public WAN IP addresses to/from private IP's i.e NAT ,  as well as determining where/if to route incoming packets on the WAN.