I've seen videoclips of Chinese tv shows & I've noticed that many of them have Chinese captions. Is that for the hearing impaired? Or is it that hard to understand spoken Mandarin?
Keep in mind that the majority of Chinese are not native speakers of Standard Mandarin. A massive government survey completed in 2004 found that only 53% of all Chinese can speak Putonghua. Doubtless the number who can understand it is higher, but it's still far from 100%. The figure is highest for urban dwellers and younger portions of the population, who missed having their schooling disrupted by such hiccoughs as the Cultural Revolution or Great Leap Forward.
China's claim to a 90% literacy rate is doubtless exaggerated, but even so there's still a significant number of people who can read Standard Chinese better than they can understand it spoken. That's the case for me, so I very much appreciated the subtitles. In particular, they were indispensable for watching the Opera Channel.