I've had this thought for a while and just wondered:
Why spend £2000+ on a router when I can just grab a decent Quad / Hex core PC (i7 etc and run Linux or a OS capable of routing and save myself loads of money? Or even a beefy server (price relevant of course)?
Basically, what makes a router so special over a normal CPU running routing protocols, NAT, etc?
The difference is in the support and features. Many of those very expensive routers have many enterprise features that you won't find in many standard OS flavors. Also, many of those routers come with the capability of supporting specific modules or expansions such as integrated gigabit fiber ports, T1 or other WAN interfaces, etc. This isn't something you can just plug into your desktop computer system.
If you want to do routing on a computer, yes, it's possible, but generally it's going to perform more on the level of a SOHO router than an enterprise class router, and you're going to have to support it yourself instead of having a full company support behind the product.
Ignoring your first paragraph though, which are all valid points and reasons. Which would be the most powerful. I.e: Which could perform more NAT translations and handle more connections for the same money? I'm not worried about support or expansion capabilities, more about raw processing capabilities.
I guess what I'm asking is shall I buy a Ferrari with blue-tooth and Sat nav, alloy wheels, leather seats.... when all I care about is speed and could get the same 0-60 results from a 2nd hand Caterham 7?
Honestly I just don't have enough experience and skill with configuring routers or building my own routers to answer your question fairly. While yes obviously the computer system is going to have more performance in raw CPU computational capabilities, that doesn't mean it's necessarily going to be faster. After all, the router hardware is completely optimized, along with the software running on that hardware, for performing the specific tasks while your desktop hardware might not be nearly as fine tuned and efficient at doing so.
In the end, your comparison of using a computer to do enterprise routing might be more like using a dump truck to move one bag of sand. Yes, it's going to get from point A to point B, and sure it has plenty of power to do so. However, that's not the type of load the dump truck is really designed for and might not be near as efficient to move it as a wheel barrel.
Why so much for a router? Look up the fabric to see what the capabilities can handle such as packets per second. BTW look at Microtik's selection http://routerboard.com/ there is the learning curve, but well below the cost of some overpriced EQ. ....Just my $.02.......
I forgot to add: The small WISP I worked at had 2500+ email users and hosted 193 domains and FTP storage sites. Our connections were 2 x 100 M CIDR, from AT&T and Quest. Our router was the Cisco 3800 series and never had a problem. The business model wasn't working out so the owner sold out to a new company that hated Cisco and it's prices. They used the Microtik solution and had a 1G connection router thru Brighthouse and another 500 M at another location router thru AT&T both connections used a $1000 Microtik router at both of their demarks, They never had a hiccup, I know I stayed till the transition was completed. BTW they had 10 times the amount of customers we had.....Our router brand new was over $15K new, theirs? $995 and it could smoke the Cisco box any day!