The term "true combo" often gets thrown around on these boards. So... why is this so hard for people? In terms of smash:
"True combo" = String of inescapable hits
"Combo" = String of escapable hits through DI (hitstun is high enough that you cannot airdodge)
"Getting hits through mindgames" = getting hits through mindgames
The last of the three could be tech chasing, or it could be aerial chasing, or anything in between, but I think everyone will agree that hitting an airborne foe is not tech chasing, as several people in this thread have insisted, seeing as they were never given the chance to tech in the first place.
The thing is, in melee, a lot of the time "aerial chasing" was still considered "comboing,"as there were much fewer options given to the character getting hit, even if they were out of hitstun. You could air dodge out of some uair chains, but the air dodge left you helpless afterward, and against a character like fox, you would end up getting hit again anyway due to his faster falling speed and being able to land and attack again. Essentially, the only way you were going to get out was either to hit the fox or to smash DI the first hit of a uair. Since most characters didn't have much priority below them, hitting fox was out of the question, and so fox could continue hitting them as long as they didn't smash DI. In brawl, if fox tried to do that to a character that ran out of hitstun before he connected with another uair, they could just air dodge it, and then they still have all their aerial options available to them, and could even hit fox afterward.
Melee had many many combos by this "smashified" definition, and it even had its share of true combos, too, that there was no way you were getting out of it regardless of what you did. Granted, there weren't many, but they were there. In brawl, there are very few combos - true or not. Almost every "combo" is just getting hits through mindgames. If your foe doesn't know that they can airdodge out due to the attack not giving as much hitstun as they thought, or that their dair beats your uair, you might "combo" them due to their insufficient knowledge of the matchup, but this will almost never work on someone who is actually familiar with the game. It's almost a backwards progression. As two players grow in skill, they are able to punish each other less and less for the mistakes they make. They're making less mistakes, but they're not suffering any heat for making them, either. In melee, two players each growing in skill would make less mistakes all the same, but they would get punished harder and harder for making them, giving them a lot more incentive not to screw up. Brawl is too forgiving about this stuff. Players who thrived on punishing their foes for making mistakes, although they can still do that, are rewarded much less for it, while the game instead rewards players who camp more than anything. If you can successfully trick your opponent into getting hit 10 times in a row, more power to you, but it won't be comboing. It's all one big mindgame. Chasing a foe for consecutive hits has essentially replaced what every melee vet might consider a "combo."