The distinction here is between Kansai and Kinai. Kansai, you are correct, is commonly associated with Osaka-ben and earthy boisterous Osaka culture. That is mostly a legacy from the Tokugawa period when Osaka became a huge commercial center dominated by merchants.

Kinai is kind of a subregion of Kansai but without the down-to-earth overtones; it's essentially Kyoto. Kyoto-ben is supposedly more elegant and refined than Kansai-ben because it more closely resembles the Japanese used by the imperial court.

Kanto-ben became standard Japanese because 1) Edo was the political center of Japan during the Tokugawa period and 2) the Meiji government established a new modern capital in Edo/Tokyo and declared Kanto-ben "official" Japanese.

A few points:

• What we generally think of when we think of Kansai-ben is the dialect of Osaka, which until the modern era was the traditional economic center of the country. I think that most would say that Kyoto-ben sounds more refined than Osaka-ben. And even then we're talking about the descendant dialect of the commoners; the nobility had a related but distinct dialect.
• The Edo dialect became the prestige Japanese dialect following the transfer of political power there under the Tokugawa, although even then this took quite an amount of time. I'll quote Shibatani Masayoshi, The Japanese Languge: "Even when the seat of government was transferred to Edo (presently Tokyo) in 1603, the status of the Kyoto dialect did not seem to be threatened immediately, for Kyoto and its neighboring city of Osaka comprised a cultural and economic center, which dominated the rest of Japan. However, this linguistic dominance of the Kyoto dialect gradually eroded as Edo began to assert its political and economic force and to develop culturally as well. Inasmuch as the contrasted language of glossaries of local forms identifies the standard form, we can conclude that the Edo dialect usurped the authority of the Kyoto dialect as the standard language around the end of the eighteenth century"
• Even then, the Kanto/Kansai distinction isn't quite as clear as it would seem. The Tokyo prestige dialect was heavily influenced by the former Kyoto prestige dialect and is really a mixture of that and the local dialect.
• Finally, what we consider "standard" Japanese is largely a result of attempts by Meiji era officials to stamp out local dialects. And while it was developed from the Tokyo prestige dialect, that dialect was not necessarily dominant outside of formal circumstances, then or now. You'll find plenty of local Tokyoites speaking Japanese just as "dirty" (to use the Japanese description) as the Kansai-ben you reference.

Well, during the Tokugawa Shogunate, Edo was the center of the government, population, and a lot of business. It's where people looked to for sophistication and power, so that's the speech people interested in those issues emulated. The imperial family was deliberately kept isolated and without power in Kansai, and virtually nobody knew how they spoke even to imitate them. The way the imperial family spoke at that time was so different from the way anyone else spoke, that it was almost incomprehensible. It was of a completely different category of speech so it was not influential on anyone's daily speech. I'm not sure why you say that the Kanto dialect is associated with the imperial family. They are associated with their own formal speech.