We can. Pence's problem is that the 19 other laws were largely passed well before the recent and dramatic swing toward support for gay marriage — and after a similar bill was vetoed by the Republican governor of Arizona.
In 2011, support for same-sex marriage passed 50 percent in Gallup polling, the same year that New York's legislature passed a law allowing marriage in that state. New York was still at the front end of the wave of states approving gay marriage; to that point, the trend had mostly been the opposite. When the federal government passed the Religious Freedom Restoration Act in 1993, a bill that made the same accommodations that are seen in Indiana's bill, a number of states echoed it. By 2003, 12 of the 19 states to which Pence referred had RFRA-like bills on the books. By the time the Supreme Court weighed in on two key gay marriage questions in June 2013, the total was 18 — only Mississippi had yet to pass its similar law.
Shortly before Mississippi's measure was passed, a national outcry arose over a bill that passed the legislature of Arizona. Ultimately, then-Gov. Jan Brewer (R) rejected that measure, after weeks of boycott threats from organizations and corporations concerned about being seen as friendly to a state that allowed businesses to deny service to gay couples.
Pence and the Indiana legislature did something similar to what those 19 states had done, but in a moment that included more scrutiny on gay issues and after public opinion had shifted away from blocking the rights of gay couples. Whether or not boycotts and outrage will extend to the other 19 states remains to be seen, but, by planting its stake in the ground at this moment, it's obvious why Indiana is already seeing such a backlash.