I found a couple problems.
A) There is a heat-sink, but the fins are perpendicular to the case vents (and airflow).
B) The heat sink is held on by a thermal pad by very low force springs
C) There's no fan for the heatsink or for the case, so the airflow stagnates.
It turns out that the Linksys, Trendnet and Netgear switches are all the same HW. BCM839x switch on a chip, BCM87xx PHY, and some circuit traces.
The reason the 100mbit switches were so much more reliable is because the 100mbit roboswitch chips from broadcom are rated for "industrial temperatures" which they list as -40C to +85C.
The BCM839x gigabit RoboSwitch chips are NOT rated for "industrial temperature". They're rated for 0C to 40C operating. Their storage temps are -40C to +70C.
Just so you know, 40C is 104F. Hot, but not SUPER hot. Easily reachable under load.
Of course, replacing the heat sing with a copper, active cooling, low profile heat-sink and fan would void the warranty, but it would increase the life span a whole bunch.