Why capitulation? Because Osama doesn’t mention jihad in the tape, and his offer of “leave us alone and we will leave you alone” goes against jihad ideology. From MEMRI:
Progressive columnist Dr. Mamoun Fandy wrote an article in the Egyptian daily Al-Ahram titled ‘Bin Laden Votes for John Kerry: A Tape of Admission, Voting and Capitulation.’ The following are excerpts from the article: 
‘Osama Bin Laden Announced his Vote for John Kerry’
“The new phenomenon in the U.S. elections is that non-Americans are voting in the elections in the hope of changing America’s course. [ U.N. Secretary-General] Kofi Annan, for example, voted for [Senator] John Kerry when he criticized [President] Bush’s policy in Iraq and described the invasion of Iraq as an illegal action. On the other hand, Iraqi Prime Minister Ayad Allawi voted for Bush in his recent visit to the U.S. when he thanked the U.S. and its president in [his address] to the Congress and in the White House. Recently, Osama bin Laden announced his vote for John Kerry in his latest tape, which was presented to us by the political porn channel [i.e. Al-Jazeera].
“The most important thing in the tape is his sincere admission that he is the man who had planned the September 11 attacks. He specified the motives that justified this operation, which began to ferment in his mind since Israel’s invasion of Lebanon in 1982″¦
“The main point in this case is that Osama himself admitted to carrying out the operation which his friends and disciples were denying for a long time. And here we have evidence, in sound and image, that the man [i.e. bin Laden] is the primary [party] responsible for the events of September 11 and that neither the Mossad nor the CIA were behind the [events], as the low-ranking [Arab] commentators have claimed. Nor the Serbs, as the senior political commentators have claimed.”
‘Bin Laden Does Not Refer at All to Jihad in This Tape’
“The second point is that the tape is one of capitulation and bankruptcy, and not one of threat and warning, since bin Laden appears in regular robes and not in a military uniform with a rifle on his side. Bin Laden has relinquished his military [character] and his arms. This, of course, is intentional on the part of the public relations administration within Al-Qa’ida and outside it.
“In addition, bin Laden does not refer at all to Jihad in this tape. There was no [mention] of Hadiths or of Koranic verses, and not even a mention of the month of Ramadan, which we [mark] today. The tape is devoid of religious manifestations and is devoid of any [mention] of the conflict between East and West, or [the war of] the Mujahideen against the infidel Crusaders, whether Christians or Jews.…
“The tape tells George Bush: ‘Leave us alone, and we will leave you alone.’ It is obvious, from both the language and the body language, that this is a speech of a man who is capitulating, withdrawing, or trying to ‘change his spots’ from a Jihad fighter to a politician. This tape resembles the announcements of commercial companies which are going out of business….”