Your phone doesn't store the password, it has some kind of session key. I would have expected it to be invalidated when you changed the password, but apparently Google doesn't do that. You'd have to ask them why.
Are you sure that you are not seeing locally cached data? I just tried it my self and changed my Google password. Directly afterwards the GMail app wasn't able to send or receive any mails on my Desire with 2.3 custom ROM.
Warning to everybody who want to verify this on his own: If you try this on your own remember that you can not change your password back to the original one. Google saves it and you can never use it again!
Robert 2012-07-16 18:13:52Z
等什么？你永远不能改变它？您是否有关相关支持DOC的链接？ R R 2012-07-16 20:15:39Z, License: CC BY-SA 3.0
我不知道是否有任何支持Doc，但您可以尝试：只需转到密码更改提示符，您将显示一个警告。 Erik 2012-07-16 22:51:09Z, License: CC BY-SA 3.0
我已经阅读了一个论坛中，密码历史记录不仅仅是最近的10个密码，因为它在企业环境中常见。 Robert 2012-07-17 07:25:02Z, License: CC BY-SA 3.0
Wait what? You can never change it back? Do you have any link to the relevant support doc? R R 2012-07-16 20:15:39Z, License: CC BY-SA 3.0
I don't know if there is any support doc for that, but you can try it out: Just go to the password changing prompt and you will be shown a warning Erik 2012-07-16 22:51:09Z, License: CC BY-SA 3.0
And I have read in a forum that the password history is not just the last 10 passwords as it is common in corporate environments Robert 2012-07-17 07:25:02Z, License: CC BY-SA 3.0