TV shows used to give work for actors at the beginning or at end of their careers. Jumping board for young unknowns, retirement shelter for washed-up has-beens. Their entertainment value was accordingly measured. That has shifted (to realize how much, check how many of the first X-files episodes you can watch and compare the experience with what you get from a just below-average show of today). Although it's old news that TV shows have caught up with feature films in prestige and surpassed them in quality, it's still quite rare, and therefore feels special, when an A-movie actor appears in one.
