Nothing lasts forever, so your premise (That Apple will "eventually" lose tablet dominance) is probably correct, although for me to give any points you would need to define a time frame. It doesn't count if it happens in 100 years. I also predict Microsoft will eventually lose desktop dominance, it might take a millenium or two, but it will happen.
If we're going to talk dominance, we should define what we mean by that too. Unit sales? Profitability? Technological leadership? User satisfaction scores? So far, I think unit sales is the only one that you have a shot at winning on in the next several years, and even then only when measured as a OS platform. While Android may outsell iOS at some point, it is likely that the iPad will continue dominance over the rest of the table market for quite some time (like that best-selling iMac).
In regard to open systems always winning, I guess I missed the turning point when the iPod was no longer the dominant portable music player. Nope, just checked and they are still at 90% market share.
I don't want to make the logic mistake of assuming that past events predict future events, but there are MANY parallels between the iPod and the iPad (apart from the similar names). Both were products that entered an established market "late". There were established market leaders that had managed to carve out small niche markets although they had not been able to achieve broad mass-market success. Many analysts predicted the failure of Apple's product prior to the launch. Upon launch, all existing products in the category were suddenly rendered irrelevant and the "competitors" were sent back to the drawing boards to start from scratch. Within the first several years of Apple's product launches, the market was flooded with cheaper products, many with better "specs", and they barely made a dent in Apple's market share. We have now reached that proverbial fork in the road, and the question is if the table market will go the direction of the iPod market or the direction of the iPhone market. I'm predicting the IPod market because of the key difference between the iPod and the iPhone. Limiting the availability of the iPhone to ATT lost Apple a lot of potential customers to Android, particularly on Verizon. Living in an area that does not have ATT service I know that I lot of people got an Android because it was the closest thing to an iPhone that Verizon offered. That gave Android a toehold in the market that they would not have had otherwise. The iPad doesn't suffer from the same problem.
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