Personally I would never apologise. You very occasionally get the odd pax who will put a bogus claim in for compensation due to a 'hard landing'. It certainly would not help yourself legally if you went out afterwards admitting it was a hard landing. You might even go give an opportunist passenger the idea to make a complaint and claim by going out and apologising.
Easyflyer83 my partner who is crew also used to have the same bug bear as you until I pointed out its usually the only opportunity passengers have to thank the pilots due to the current climate of locked door policies. If I'm a passenger and receive a great service in flight from the cabin crew I will usually take the opportunity there and then to thank them and say bye to them disembarking and then thank the flight deck. Sometimes it can be the other way round where you land in challenging conditions and passengers will thank the cabin crew and ignore the pilots. Don't take it to heart!