Classic servers are clustered also. there are 3 classic servers, Ector, Lamorak and Gareth, but they are all clustered together.
The only non-clustered servers are the alternate ruleset servers, Mordred and Gaheris.
Classic is a bit misleading. They did not leave off at any expansion. The original name was something of Non-ToA server. The classic servers only have 4 differences from the normal servers.
1) No Master Levels
2) No Artifacts
3) Concentration buffs must be cast by a group member (i.e. no buff-bots).
4) No /level ability
Trials of Atlantis regions don't exist, but the newer expansions (Catacombs, Darkness Rising and LoTM) all have ToA bonuses on the items. It is getting very close to having templates as good as normal servers, but no buff-bots, arties or Master Level abilities helps even the playing field a bit for casual players.