You seem to know a lot about what's inside the smoke detectors here.
You didn't notice me taking one down to look at during the visit last year?
I have an extended family member who works in the industry, so some of my information here may be more specific to his brand of detectors. They also mostly specialized in CO detectors which did have pretty terrible useful lifespans early on. 7 years now is a big jump over the initial 2 years for CO sensors.
I did find this to explain what the test button does on an ionizing detector such as yours.
http://diy.stackexchange.com/questions/24552/what-happens-when-you-test-a-smoke-detector There is also the lawyered up description in the patent for one method of testing these types of detectors.
http://www.google.com/patents/US4456907I believe your test results using moving air over the sensor may be due to this note later in the Wikipedia article comparing ionizing to phtotelectric smoke detectors:
Also, ionization detectors are weaker in high air-flow environments, and because of this, the photoelectric smoke detector is more reliable for detecting smoke in both the smoldering and flaming stages of a fire.
Clearly the burnt toast test is proving something still works for yours though.
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