I think what you may not be taking into account is the product life cycle of a console system, and where we currently are in that cycle.
Smartphones and tablets (and "phablets") are on an entirely different life cycle, being constantly improved and newer generations always being released. A smartphone or tablet is generally expected to last two years, more or less, before it is replaced by the next generation version of the product.
Consoles, on the other hand, are expected to last about five or six years before they are replaced by the next generation. The current Xbox and PlayStation systems are in the final stages of their current life cycles, and are only receiving minor upgrades until their more highly developed replacements are put on the market.
Though I understand that some smartphones really pack in some power, none will ever match the processing and graphics performance of whatever next-generation console system hits the market. Let's forget about Nintendo consoles for a moment here. A top-of-the-line smartphone or tablet may be able to perform about as good as the dozen-year-old PlayStation 2 or original Xbox, but it'll never be able to run the latest Elder Scrolls game in the way that it runs on the latest generation of those systems.
As for Nintendo -- well, Nintendo isn't after the "hardcore gamer" market, and their games may very well perform as well on a tablet, if not better. Perhaps this is one reason Nintendo is expanding into the tablet market, in a sense, by making their console controller a tablet itself. ("If you can't beat 'em, join 'em!")
I thank you all for your opinions!