Burning Valves in the 3 cylinder engine

I quote from another thread post...."The car finally burned a valve (due to my ignorance
on needing to keep the egr passages cleaned)...."

I was wondering about the infamous exhaust valve on the first cylinder while
I was driving into work today....

Mine burned out at 150,000 miles and I understand that that is normal for the
Geo Metro 3 cylinder engine.

Why?

What is there about this engine such that this exhaust valve business happens on cylinder
number one?

And does the EGR Valve and passages have something to do with that?

If so, I now know how to clean the EGR Valve and Passages out with that
spring device I invented last Fall.
http://www.automotiveforums.com/vbulletin/showthread.php?t=622536&highlight=carbon

DoctorBill

DOC;

My understanding is that by reintroducing a certain amount of exhaust gas into the cylinder it not only reduces the emissions by reburning the exhaust gas but it helps moderate the cylinder temperature.

My interpretation of this is that as the engine ages (typically 100K+ miles) and combustion efficiency decreases; you tend to get carbon build up in the cylinder due to ring wear/blowby and if the egr passages get blocked then as the temp in the cylinder climbs the carbon deposits create a hotspot which eventually "burns" the valve. Keeping the egr passages clear and occasionally de-carboning (SeaFoam, GM top cleaner, etc...) will help to avoid these issues.

Anybody else want to add/correct this description?