I do this all the time. What point are you trying to make exactly?
http://www.scubaboard.com/forums/images/smilies/More Smiles/shakehead.gif Are you in some way inhibited from breathing without a plastic tube in your mouth?
The point I'm making is that it's a lot easier to navigate through a kelp bed on a surface swim by going through it face down while breathing through a snorkel. Sure I could do without the snorkel and breath hold face down and take a breath in from the side once in a while but why? snorkelling allows me to breathe steadily.
Rolling over on your back and trying to go through kelp, the first thing that happens is your tank valve will get hung up in the kelp, and when you roll over to see where you're going the kelp gets wrapped up on your rig even worse.
It's easiest to go over and through kelp face down and pick a path through the thin areas or to push it under you and allow it to slide under your front side which has way less entaglement points than your back side.
I guess a person who absolutely hates snorkels with a religious ferver could crawl over kelp face down with reg in mouth but I prefer to save my air for the dive and I don't always want to start my dive right in the kelp bed in 15 or 20 feet of water, I like to go out a little further out before I drop. Our bottom typography is a lot different from Socal also. It's not always possible to drop down and go under the kelp close to shore due to the radical terrain and giant rocks.
We don't have long sloping beaches and low lying shelf reef like Socal, our terrain is much more radical and treacherous.
Your kelp beds are not the same as what I dive in. I dive North of SF on the North Coast.
I've dove Malibu: Leo Carrillo, Deer Creek, Refugio, El Cap, etc.. I've also dove Catalina. A few strands of giant kelp here and there is not what I'm talking about. Try going through a bed of well developed North Coast Bull Kelp sometime. I freedive in the stuff too.
A snorkel is a great simple easy to use inexpensive piece of wonderfull dive gear that makes surface swims a pleasure.