American Troops in Japan, are they still necessary?

According to Navy Times:

Prime Minister Yukio Hatoyama suggested Thursday that he would give up the idea of meeting one on one with U.S. President Barack Obama in Copenhagen next week to discuss the relocation issue of a Marine Corps airfield in Okinawa, after Washington shunned the Japanese leader’s overtures.

Yomiuri Shimbun on the Futenma issue says this:

Bilateral ministerial-level talks on the issue have been suspended. This is because the Japanese government conveyed to the U.S. side its intention to postpone the settlement of the issue by the end of this year due to opposition from the Social Democratic Party--one of the junior coalition partners of Hatoyama's Democratic Party of Japan--toward the current relocation plan within the prefecture.

Washington, meanwhile, has notified Tokyo that it would postpone bilateral talks to "deepen" the security alliance, which had been planned as next year marks the 50th anniversary of the revision of the Japan-U.S. Security Treaty.

Hatoyama agreed at a summit meeting with U.S. President Barack Obama last month to "expeditiously" solve the Futenma relocation issue. But the prime minister then unilaterally decided to give up settling the issue before the new year due to domestic circumstances. Moves like this are unacceptable if the two nations seek to work together based on a relationship of trust.

The government must give serious consideration to how crucial it really is to postpone a settlement of the issue within this year.

If the government fails to solve the issue before the end of the year, the current relocation plan would effectively be shelved. It also would be extremely difficult to find an alternative site and the process as a whole would certainly take a great deal of time.

If this comes about, the Futenma base likely will continue for years to expose local residents to dangers due to its location in a densely populated part of Ginowan, and could even end up staying at its current location indefinitely. It also would increasingly risk the collapse of a plan to transfer 8,000 U.S. marines to Guam and return six U.S. military facilities to the nation.

But while the editors of the Yomiuri are not happy with Hatoyama, he's finding some sympathy in a Futenma related editorial published in the New York Times.

My conversations here suggest Hatoyama’s not going to make a final decision for months, perhaps not before upper house elections next July that could liberate him of his left-wing junior coalition partners. Richard Armitage, a former deputy secretary of state who’s been running around town, is only the most visible expression of U.S. impatience. Obama shares it.

“I can’t change the political situation here,” Nagashima said, referring to the Okinawan anger and coalition pressure on Hatoyama. “I really want our American friends to accept and work with us despite these difficulties.”

That’s sound advice. Having just taken 90-plus days over an Afghan decision, Obama can’t dismiss Hatoyama as a ditherer. He’s taken the reins after more than five decades of the L.D.P shogunate. He needs time — and the whiff of a campaign financing scandal is not helping him.

The deeper forces behind Hatoyama’s victory and the Futenma imbroglio are these. Japan, like Germany before it, wants to move out from under American tutelage. Unlike Germany, however, it inhabits a part of the world where a Cold War vestige — nuclear-armed North Korea — endures and fast-rising China with its growing military is just across the water.

In short, the need for the Japan-U.S. alliance is real even if the Japanese urge for liberation from its more demeaning manifestations is growing. That says to me that everyone should take a deep breath. U.S. impatience should be curbed along with the pie-in-the-sky “world of fraternity” musings of elements in Hatoyama’s party. Be flexible on Futenma but unyielding on the strategic imperative binding America and Japan.

Hm. Okay. Here are some questions:

1. At what point will US troops in Japan become superfluous, if they aren't aleady?
2. Are they there only as a symbol of an alliance or do they actually have a security purpose?
3. Is the tatemae reason mostly North Korea, while the Honne has more to do with China and America's growing debt to China?
4. What would happen to the alliance in general if America's economy were to implode (at least more than it has already)?