Actually, the old A's owner Walter A. Haas was all cool with the Giants moving down to San Jose in the '80s when the Giants were struggling like hell with attendance at the frozen dump of Candlestick Park. It's not surprising. He saw the opportunity to watch the cross-bay rival team pack up for the southernmost population center of the Bay Area, and doubtless looked to see the influence of the A's touch the city of San Francisco. This was when A's were the dream team of the Bay, having threepeated in the '70s and building toward their run of three AL pennants in a row in the late '80s. Even if one wishes to believe it was some magnanimous gesture on Haas's part, and not a very transparent move based on business calculations at the time (lol), he's not who's in charge of the A's now. The odds are that the current group of A's ownership is like the other 29 owners: they look out for their own interests. (As a point of fact, Lew Wolff will doubtless sell the team off the moment he hypothetically gets his real estate bonanza put together, with an eye toward creating a television deal that would sweep from the South Bay to San Luis Obispo to create an empire of media saturation through much of central California. If the Giants would simply give up San Jose now, it would doubtless make the A's happy. But if the rabble-rousers in Fremont didn't destroy the plans for Cisco Field there, that would have pleased the A's. If the haughty landowners of the 66th Avenue area would have sold their land, this would have pleased the A's. There have been quite a few respective entities blocking the A's from doing what they want.
What gets lost is that nothing can be done about a move to San Jose now without the agreement of MLB's owners. All it would take is eight owners/ownership groups to block it, and down in defeat it would go. And it would not be difficult to find eight MLB owners who would do exactly that. Let's just say that the Angels, Dodgers, Mets, Yankees, Phillies would merely begin a strong ownership fortification against the move. Throw in ownership entities that would logically want to see the A's remain comparatively impoverished like the Rangers (and the Angels again, haha), and corralling the necessary number of owners to block it would be as easy as pie. Bud Selig is a horrible crony, but that is what he is--he's a figurehead for the owners. They call the shots, he's simply the master of ceremonies.
As for the territorial rights shenanigans, allow me to quote the San Francisco Giants' ownership group's statement, reported by one of the better Bay Area sports bloggers in Alex Pavlovic:
“The Commissioner has asked us to refrain from discussing the territorial rights issue publicly. Out of respect for his request, we will limit our response to setting the record straight on the history of territorial rights.
The Giants territorial rights were not granted “subject to” moving to Santa Clara County. Indeed, the A’s fail to mention that MLB’s 1990 territorial rights designation has been explicitly re-affirmed by Major League Baseball on four separate occasions. Most significantly in 1994, Major League Baseball conducted a comprehensive review and re-definition of each club’s territories. These designations explicitly provide that the Giants territory include Santa Clara, San Francisco, San Mateo, Monterey, Santa Cruz and Marin Counties and the A’s territory included Alameda and Contra Costa Counties. The MLB owners unanimously approved those designated territories and memorialized them in the MLB Constitution. Since then, the MLB Constitution has been re-affirmed by the MLB owners – including by the A’s – on three different occasions (2000, 2005 and 2008), long after the Giants won approval to build AT&T Park. Mr. Wolff and Mr. Fisher agreed to these territorial designations and were fully aware of our territorial rights when they purchased the A’s for just $172 million in 2005.
The population of Santa Clara County alone represents 43% of our territory. Upon purchasing the team 20 years ago, our plan to revive the franchise relied heavily on targeting and solidifying our fan base in the largest and fastest growing county within our territory. Based on these Constitutionally-recognized territorial rights, the Giants invested hundreds of millions of dollars to save and stabilize the team for the Bay Area, built AT&T Park privately and has operated the franchise so that it can compete at the highest levels.”