Yes, they CAN sell in China, they're just at a huge disadvantage. Is your argument that because SOME products still sell, the barriers aren't significant, or that US firms aren't adversely affected by them, to the benefit of Chinese ones?
My argument is that when companies can't compete on technology as they may be used to, too frequently, they throw their hands up in the air and conclude that this means they can't compete period. However, we can see that Western companies are successful today competing along different axes.
I would even extend that further by saying that if things dry up in the future and we have to keep innovating to stay ahead as China continues to copy and catch up, good. Let's do that. Everyone will be better off.
mrb is exactly right. US companies CAN sell in China, if they figure out how to, and some have.