Everyone is afraid of getting hosed by not anticipating future rights. Everyone knows how actors lost out by agreeing to a much smaller percentage of DVD revenue than for films (because they underestimated the market and profit margins), and everyone is determined to not let that happen to them.

This kind of fear propagates faster than actual realistic fears because you sound wise by talking about the future. So lawyers can always "add value" by cautioning against some deal that might be disadvantageous in 20 years.