(Written with Madelaine Maior, Silicon Flatirons research fellow)
There’s an emerging consensus that the role receivers play in interference should be recognized in wireless regulation. But why has it taken so long to come to a conclusion about the performance of receivers?
First, though it’s an argument against interest for us to say so, there may not be a problem to be solved. Limiting the regulator’s scope to transmission permissions may be the least costly option for maximizing spectrum use. The problem of building a better receiver may just be the obsession of a few engineers. There may be no efficiencies to be gained, and there may be costly side effects of any regulatory involvement, let alone something as draconian as receiver performance mandates. 
One could also argue that while there may one day be a problem, that day has not yet come. Calls for tighter regulations are not new; for example, Allen & Garlan asserted back in 1961 that “[a]lthough the useful radio spectrum has been expanded many fold during its history, the uses and demands for this spectrum have increased at an even faster rate. Thus there is continued need for ever stricter requirements, both operational and technical, to improve the effectiveness of spectrum use.”  The efficiencies to be gained by regulating receivers will only be justified when the spectrum is so crowded that there is nowhere else to go – and we might never reach that point if technologists and entrepreneurs keep finding new solutions.
Second, assuming there is indeed a problem, it may simply be insoluble. Intractable legal problems abound; consider, for example, the perennial tension between individual rights and group rights, or the unresolvable dialectic of legal rules versus standards.  Institutional factors may also preclude a resolution (see public choice theory): regulators probably appreciate the flexibility that an ambiguous harmful interference standard provides, since it allows them to take non-technical (e.g. political) factors into account when judging interference claims between receivers and transmitters.
Finally, the problem may be solvable but the necessary techniques have not been available until now. Developments over the last decade in the definition of spectrum usage rights (SURs) using resulting signal strength metrics have cleared the way for the formulation of explicit interference limits. ,  Since spectrum management in its first century focused on transmission permissions based on emitted power at the antenna, these resulting signal strength SURs facilitated a shift of focus to receivers and the interference they need to tolerate everywhere in a coverage area.
We may also have been blocked by the incorrect assumption that regulating receivers should be just like regulating transmitters. They’re not two sides of a coin: defining and measuring receiver performance requires an understanding of the desired quality of service and minimum desired signal as well as interference power, whereas transmitters can be regulated merely by looking at radiated power. A conversation that focuses on mandating receiver performance is therefore almost always bound to run aground on the complexities entailed by adding quality of service and desired signal parameters to the regulatory mix.
 The use of industry receiver standards, as well regulatory performance requirements for specific services like television and aviation, suggest that there are at least prima facie benefits in at least some cases.
 Allen, E. W. and Garlan, H. (1962). Evolution of regulatory standards of interference. Proceedings of the IRE, 50(5):1306-1311. See 10.1109/JRPROC.1962.288087.
 Pierre J. Schlag, P. J. (1985). Rules and Standards, 33 UCLA L. Rev. 379. See http://lawweb.colorado.edu/profiles/pubpdfs/schlag/schlagUCLALR.pdf.
 Matheson, R. J. (2005). Flexible spectrum use rights: Tutorial - ISART 2005. In International Symposium on Advanced Radio Technologies (ISART) 2003. National Telecommunications and Information Administration. See http://www.its.bldrdoc.gov/pub/ntia-rpt/05-418/05-418_matheson.pdf.
 Ofcom. (2008). Spectrum usage rights - a guide. See http://stakeholders.ofcom.org.uk/spectrum/spectrum-management/spectrum-usage-rights/.