My advice is not to simply pay the license fees, but if (1) Apple and Google don't help their app developers (Apple appears to be willing to help but the extent of it isn't clear yet; Google has neither said nor done anything so far) and (2) the licensee fees are in a given case much less than the cost of even a cursory legal analysis, then they're an economically more intelligent choice unless the license agreement contains anything that poses a risk comparable to the one of being sued without a license agreement.