共3台服务器，只有管理中心所在服务器提示需要升级：
执行命令：stsadm –o localupgradestatus,返回结果类似如下：
[2] content database(s) encountered.
[1] content database(s) still need upgrade or cannot be upgraded.
[7] site collection(s) are contained in the content databases.
[4] site collection(s) still need upgrade.
[53] other objects encountered, [1] of them still need upgrade or cannot be upgraded.
解决方法尝试：
方案一：重新" SharePoint 2010 产品配置向导"，但未执行服务配置。无效
方案二：执行"psconfig -cmd upgrade -inplace b2b"，然后重启服务器。无效
方案三：分别在SP10-APP和SP10-WEB上分别执行" psconfig.exe -cmd upgrade -inplace b2b -force -cmd applicationcontent -install -cmd installfeatures"。无效
方案四：在管理中心，执行"配置向导"。完美解决。
总结：现在看来，如果方案一中执行完产品配置向导后，紧接着继续执行场配置向导，应该就能解决了。
https://social.technet.microsoft.com/Forums/systemcenter/en-US/6221ef08-f3e6-448e-ad3d-fe53b7b9cfc6/site-collections-still-need-an-upgrade-on-one-server-in-sharepoint-2010-farm?forum=sharepointadminprevious
https://social.technet.microsoft.com/Forums/en-US/15553dba-3f46-43a6-83bb-4ef94a982ae9/farm-information-status-shows-upgrade-available?forum=sharepointadminprevious
扩展：
http://www.tsls.co.uk/index.php/2012/04/27/unable-to-update-sharepoint-2010-cu-or-sp/
上面连接说，因为IIS里存在不能引用的站点，导致不能升级。实际我App服务器里确实有一个站点有问题，我将其删除后。执行方案四就好了。
但此站点不是SharePoint站点。不知道是否和此也有关