After a decidedly slow start, the satellite radio industry seems to be gaining some long-awaited traction. This week, XM Satellite Radio, the larger of the two currently operating networks, will announce that it has passed the key benchmark of a million subscribers. Sirius, XM’s only competitor, has approximately 250,000 subscribers. The significance of the million-listener mark is likely to be felt on Wall Street, where investors are expected to begin taking the industry seriously for the first time.