PB did a pretty good job but I will chime in.
1. We have to think back to the creation of Jonsered. It was originally a separate company with unique models. Following the acquisition by whatever the husqvarna conglomerate was back when, the husqvarna models were folded into the jonsered line. The jonsered brand still has a strong following in some areas, and certainly with some users. Some people don't openly acknowledge or don't know that they are internally all but identical to husqvarna, at best they may admit some sort of collaboration or similarity.
In many places, you have a Stihl dealer, a husqvarna dealer, and then a more "off" or "smaller" brand dealer. At least locally here I do. Some echo, some jonsered, maybe some dolmar, shindaiwa...smaller lines. If you get rid of jonsered, husqvarna loses that shelf space in all those dealers. Nobody is going to want to open up a husqvarna dealer right next to a husqvarna dealer. More dealers in the same place is a good thing.
2. Normally industry market share is closely guarded--maybe bob can chime in with something that's been presented at a trade show. The closest thing I have seen, which was a preference poll, rather than a sales poll, showed the following results:
"With over 3,100 votes cast, Husqvarna was the chain saw of choice as voted on by About Forestry readers. Here are the percentages preferred and ranked by brand of saw through October, 2001:
Husqvarna - 41%; Stihl - 40%; Jonsered - 7%; Echo - 4%; All others - 8%
As you can see, voting for a favorite saw is extremely close when separating between first and second place brands. Husqvarna and Stihl are by far the most popular saws in America."
Very imprecise, from a website, and it's preference, not sales. But maybe this gives SOME idea.
3. Not sure. Probably. I imagine with how big EFCO/EMAK is it must be pretty popular in southern europe like italy.
4. The russian designs that I have seen have been fairly archaic. In that WLC there was some eastern european saw and there was literally one participant who had them. Presumably they are technically inferior. Regarding the chinese, there certainly are various saws manufactured in china for sale and in operation--even stihl and husky have plants there. The chinese brands that I have seen are largely copies of other designs. They cant bring in a blatant copy of a stihl or husqvarna or dolmar saw and sell it here--they will be subject to patent, trademark, etc. At this point in time you have to really have your #### together to meet EPA and safety requirements--most of the chinese designed and chinese manufactured goods probably cant do this.
There are some cases of chinese manufactured goods as a brand gaining ground in the US. If you look at LIUGONG loaders, they have been able to gain some buyers because they are basically 1/2 the price of a Deere or Cat machine. Not great for a quarry, but some say they are OK for snow.