Under pressure from investors, Cablevision Systems has decided to spin off its Madison Square Garden unit as well as its MSG cable network and its sports teams, the New York Knicks (basketball) and the New York Rangers (hockey). Investors have long complained about the use of revenue from its cable operations -- which primarily cover the New York metropolitan area -- to support the sports operations. They have complained, for example, that highly lucrative salaries that have been paid to its top players have not resulted in corresponding revenue at the ticket gates. Also on Thursday, the company reported an 8-percent downturn in earnings to $87 million from $94.7 million during the comparable quarter a year ago.