While the critics are correct that the direct mandate on the states to establish regulations specified by Congress would run afoul of the cases mentioned, they overlook how easy it is to simply convert the current direct mandate language into a use of the Spending Clause as leverage to coerce the states into compliance anyway. When the federal government sought to force the states to adopt a 21-year-old minimum drinking age, for example, it simply informed the states that they would forfeit any highway maintenence funds from the federal government if they failed to do so. All the states quickly fell into line with that federal mandate. Using similar means, the federal government coerced states to adopt a 55mph speed limit during the late 1970s and early 1980s. And in South Dakota v. Dole, the Supreme Court approved these coercive uses of the Spending Power.
In this case, the federal government would only need to threaten to withhold Medicare and Medicaid funding from any state that failed to adopt the required insurance exchanges. It seems quite unlikely that any state — even those that might briefly posture in opposition as they did with regards to TARP funding — would actually accept such a price for standing in opposition to health care reform.