Jrista, you can not make valid conclusions due to the following:
1) Data is not complete. You are analysing US Amazon sales only. This data is not sufficient even for analysing US marker as there are many more internet and standard sales channels in US.
2) In order to make valid conclusions about dominance in the global market you should include all Amazon shops (US, UK, FR, etc.), B&H, retail stores and many others. Practically it is impossible to gather exact data as you will definitely will not include all sales channels.
3) It would be more reliable to gather data from Financial statements or management reports, bank analyst reports on Canon, Nikon, Olympus, etc. However, here we encounter a problem that even segment reporting data is too aggregated. These companies are involved in many businesses (e.g. Sony, Canon, etc.) and do not provide in financial statements very detailed data about some particular business segment (in our case that would be specific camara data). Of course it would be very interesting for us to see what are Canon global sales of specific cameras in different markets, what is profitability of specific products (we would see that 1Dx, 5D MarkIII are the most profitable models... by the way, it is my assumption

). However, such data would be very interesting to competitors and everybody is trying to disclose required information according to various accounting standard requirements (US GAAP, IFRS) and aggregate data in such way in order not to disclose its strengths and real position in the market to competitors. The Bank analysts are obtaining more specific data during various press releases, conf call, etc. (however that data is not audited and nobody can place 100% reliance on it). For example, if you take market position (in percentages) from different companies (I am talking about their own assessments), add everything together I am almost sure that you get more than 100%
I am writing this as I was an Audit director for many years in BIG4 and know such things
