I am pretty sure ownCloud web client does have timezone support, but he didn't change the setting.

From http://owncloud.org/support/calendars/

> The calendar needs your current position for detecting your timezone. Without the correct timezone there will be a time offset between the events in owncloud and your desktop calendar you synchronise with owncloud. You can also set the timezone manually in the personal settings.

After reading the article, it seems like the author hasn't looked too hard into self-hosted solutions.