They could but they don't want to. This is the classic approach to killing something you are opposed to on principle but you realize your principles are very much a minority statement.
So instead of saying:
"I believe that copyright laws are ridiculously inappropriate for the Internet, and should not be applied or enforced. Everyone should be able to upload/download as they please."
which would not be a winning approach, because the vast majority of people would not agree. Nor do their elected representatives.
"This will break the Internet because (some sound bite on DNS, DNSSEC, and other technical stuff) !!!! You are stupid and you don't understand the technology!"
Essentially Rep. Smith is calling their bluff. He's saying, let's pass the bill but not implement it until we can do a technical study. The technical study would ASSUME that we WANT to block access to infringing overseas web sites, and DIRECT that a technically sound approach be put in place. That is, it would lay the requirement to implement the use case on the technical committee. If it breaks DNSSEC, or other things, well, fix that with a new technical proposal, is what he's saying.
I personally believe from a technical POV that it is possible to do this. I think the Internet community is resisting this on principle because they do not believe the use case is appropriate. But they are pretending that it can't be done.
It'll be interesting to see how this plays out. My opinion is that the Internet community, by being so rabidly opposed to SOPA, is missing a chance to mold and direct this into something useful and appropriate for the Internet. If all the Internet community does is rant and rave, SOPA or son of SOPA will be jammed down their throats eventually.
Why? Because of the economic and political imperatives surrounding it. NOT because the evil nasty content owners who bribe the politicians. That's ridiculous. You are laboring under the illusion that stopping piracy is unpopular. It's not.