After a year of seemingly shouting in the wilderness, Paul Volcker finally got his druthers this morning. The Obama administration is going to push for a breakup of modern Wall Street. Or at least a bunch of restrictions to wall off risky, profitable stuff from the nuts and bolts that keep the financial system going. Which may not be able to get through the Senate anyway. In fact, failing to get this through the Senate may be exactly what Obama’s political strategists want—a popular cause to bash the Republicans with in the fall midterm elections.

But let’s take the (still-pretty-vague) proposal at face value. It would restrict “the market share of liabilities at the largest financial firms” to what they are, um, now. And it would

ensure that no bank or financial institution that contains a bank will own, invest in or sponsor a hedge fund or a private equity fund, or proprietary trading operations unrelated to serving customers for its own profit.

So my question is, what did hedge funds, private equity funds and proprietary trading operations at large banks and investment banks have to do with the financial crisis we just went through? Not a whole lot, as far as I can tell. Yeah, there were those two Bear Stearns subprime-mortgage hedge funds that imploded in the spring of 2007. But they would have had about the same impact if they weren’t linked to Bear. Maybe their collapse inflicted reputational damage that hastened the fall of Bear Stearns almost a year later.

But beyond that, the biggest troubles at the big banks and investment banks had to do activities that were related to serving customers. All those toxic CDOs that weighed down Citi and Merrill and UBS were intended to be sold. It’s just that customers stopped buying at some point in 2007.

And the trading profits that have been resulting in big bonuses at Goldman and JP Morgan are for the most part not from separate proprietary trading operations, but from trading done (ostensibly at least) on behalf of customers. Wall Street firms don’t charge much in the way of commissions on the securities, foreign-exchange and derivatives trades they arrange with their customers. Instead, they find ways to profit from the trades even as they “serve” their customers. It seems like a weird, conflicted way of doing business, but it also seems like it would be really hard to stop without going back to some sort of regulated-commissions regime—and it doesn’t appear to be something the Volcker-Obama effort is targeting.

Maybe the answer here is that the specifics don’t matter. By the 1990s, the specifics of the Glass-Steagall restrictions on commercial banks seemed pretty nonsensical—but I’ve heard from enough people on Wall Street that doing away with those restrictions unleashed a wave of crazy risk-taking to believe that they must have had some kind of sobering effect. Just having some kind of wall between the risky and essential helps, even if that wall isn’t constructed in exactly the right location.

Update: John Carney reports that Wall Street firms are already contemplating ways to reinvent their internal hedge funds and such as “operations … serving customers.”