Don't listen to most of these people. They are not following the rules.
If the Fighter kicks in the door BEFORE combat occurs (and before initiatives are rolled), then the creatures inside the room ARE aware of the creatures outside the door and there is no surprise round. By definition. It is only if the Fighter does NOT make the opponents aware of the party that a surprise round occurs. If he makes them aware with a pre-combat action, then by definition, both sides are aware.
SURPRISE
When a combat starts, if you are not aware of your opponents and they are aware of you, you’re surprised.
If the Fighter opens the door before combat, then the NPCs are aware and no surprise round. It is only if the Fighter opens the door within the surprise round that the party even gets a surprise round.
Hence, your DM did fine. He seems to know this particular rule pretty well.
Surprise round. Roll initiative.
1) Cleric
2) Rogue
3) Fighter
4) Wizard
Cleric delays (or readies), Rogue delays (or readies), Fighter kicks in door, Cleric (or Rogue) goes, Rogue goes, Wizard goes, first round starts.
This is not real life and the first guy in the SWAT team does not necessarily get to be the first guy through the doorway (except possibly for a 5 foot step). This is game rules we are discussing.
The problem here is that some other posters are allowing the PCs to get an action in (kicking in the door) for free which would alert the other side. So, let the players decide. If they want the surprise round, they cannot do anything before the surprise round to alert the NPCs (possibly including casting spells as per the example in the DMG, but also by kicking in a door). If they do not want a surprise round, then open the door and then have everyone (PCs and NPCs) roll for initiative in round one as normal.
Would people allow the PCs to do some other NPC alerting action instead of kicking in a door like casting a Fireball and STILL get to act on the surprise round? If not, why do they allow them a free action of kicking in the door?
Note: In the "open the door pre-combat" scenario, the DM might still have a Wisdom roll (or Listen check or some such) for the NPCs to see if they are able to react and if any of them fail the check, then he could still have a surprise round. However, such a DC should be fairly low (DC 5 to maybe DC 10 max, depending on how alert they are, if some are asleep, obviously the DC should be much higher). It is not so much to hear the door crash open as it is to be alert enough to react to it. In this case, having the Fighter get another action in during the surprise round would be ok, but several of the NPCs might possibly also get an action in during the surprise round because they were alert.