The most intense debate in television today—whether the lure of Netflix and YouTube is causing viewers to disconnect their cable-TV service—is likely to intensify after new figures showed a slight decline in overall pay-TV subscribers in the second quarter.

Publicly traded cable, satellite and phone companies had a combined net loss of about 200,000 subscribers in the quarter, earnings reports showed, about 0.2% of the roughly 100 million pay-TV subscribers. Sanford C. Bernstein estimates the overall industry shed more than...