campy lost their lead in the high end road bike market when Shimano came out with SIS and STI and campy couldn't respond for a while. Campy's index shifting was terrible for the first two iterations. However, they seemed to do well with their first Ergo lever (which was serviceable from the get go). To put it in relative terms, Suntour went out of business because they couldn't get their act together with index shifting. And their slant parallelogram derailleur design is what made SIS possible (Shimano had to wait till the patent expired to do SIS). everyone uses Suntour's derailleur design since it's no longer covered by patents.
Now Campy is back on it. the only thing is that Lance caused them to lose their first Tour in God knows how many years. So I'm rooting for whoever is riding Campy next year.
regarding company size - Shimano is huge compared to Campy. I believe Campy does worldwide less than Shimano does in Europe. Something like that. Shimano also does a lot of other things - like make gears for Saturn transmissions, really nice fishing reels, etc.
campy also never did low end stuff well. so they couldn't compete with mountain bike stuff. ditto lower end road bikes. so the masses have (and know) shimano. most shops don't stock $2000+ bike exclusively. however,
like others pointed out, if you go to a group ride or a race, you'll see a lot of Campy.
cdr