First, your points are pure conjecture. There is no information to point to for your analysis other than mere speculation based on scant information. The crafts were lost and there was no way to know for certain what the cause was. Stating as fact something that is pure conjecture is the height of ignorance and stupidity. You next statement made me laugh, "No one who actually works in the field of space travel is that concerned about micrometeorites. No one who reviews the spacecraft losses has concluded we've lost them to micrometeorites. And as far as I can tell, you don't even do basic research to check whether micrometeorites are an issue before talking about them." Actually, nothing could be further form the truth and is a very serious concern in point of fact. Tega Jessa just published an article on this very matter and
http://www.universetoday.com/89804/micrometeorites/ just a few months ago. If you had taken more than a second to actually read up on this subject, you would realize it is a very serious concern.
> Well a very large hole would take a larger meteorite wouldn't it? And a larger meteorite we'd be able to track and see coming. The point of micrometeorites is that they're tiny and untrackable.
And your point is what? Maybe they could detect it coming, the likelihood they could avoid something moving that fast (even if it it is the size of a fist) is unlikely. Again, you dismiss something deadly as a non-threat because of your ignorance about the matter only. Being able to see something coming at you and being able to avoid it are two different things. Something large enough to cause a space craft to decompress is not that significant and detecting it in time to avoid it would be highly unlikely.
Also, thank you for the math lesson. However, it is just a simple a display of ignorance by employing averages. If you had any understanding of this field, you'd realize a few things: 1) the amount of material is NOT insignifcant (even though you try to pretend otherwise by employing averages which is silly because of point 2) fields of meteors (and micrometeorites) interact with the earth at varying densities. There are periods of time in which the earth has little meteor activity and periods of time in which the earth interact with dense fields of meteors. We call these meteor showers.
We simply do not know the density of the fields between Earth and Mars. Given the distance the craft has to travel and amount of time (over unknown space), it is highly likely the spacecraft will encounter fields of these particles of varying sizes. Given the speeds involved, the fact is that any craft going to Mars is highly likely to collide with micrometeorites.