The difference between l-canceling and teching is this: there are times to tech and times not to tech. Choosing not to tech, for example, can occasionally be a useful mindgame and stalling tactic when you're caught in a tech-chasing chain grab. Furthermore, you can choose to tech in place or techroll to either side depending on the situation. With teching, there are strategic choices you must make every step of the way.
Not so with l-canceling. You ALWAYS want to l-cancel, because there's no point in missing the l-cancel if you are technically capable of executing it. Essentially, l-canceling's existence forces Melee players to press an extra button or suffer the consequences in higher levels of play. While this creates technical difficulty, l-canceling does not add anything strategically that couldn't be achieved by simply making moves less laggy to begin with. If SSBM did not have l-canceling but every character's aerial attacks had half the lag, all the high level strategies would essentially be the same, minus one physical button press per aerial attack.
Therefore the loss of l-canceling is not inherently a bad thing. What could make l-canceling's absence problematic in Brawl is the fact that many of Brawl's characters have an obscene amount of aerial lag and apparently have no way to compensate for it. Ganon, for example, is almost sure to be punished if he attempts any kind of aerial approach and whiffs, so there is a lot of talk about how he will be rendered unplayable at higher levels.
But only time will tell, right? While Melee-style competitive play looks a little bleak at this point, we can't say anything for sure until the game has been out for a few years. People will inevitably discover a new set of advanced tactics unique to Brawl, and we'll have to see if these new techniques can compensate for the loss of old ones. I'll be glad if Brawl turns out to have as much depth as Melee, but until then I think the best we can do is enjoy the game for what it is.