I'm always puzzled by the assumption that just because continuity exists among different works, it makes each individual story incomprehensible on its own.
I think this mostly comes from people having bad experiences with other works in the past that do get so bad they are incomprehensible on their own.
Using comic books as an example, if you are a fan of the Batman tv series and then jumped in during a random point in the middle of a major 90s arc like Knightfall it would have been horribly confusing. Some, though certainly not all, of the Star Wars novels have had this problem. Jumping into the middle of a major epic fantasy series like the Wheel of Time or A Song of Ice and Fire would not be a fun experience either, nor starting Lost at season 3 or the recent Battlestar Galactica at season 4 or a season of 24 at episode 8.
Star Trek books have been better at making good jumping on points, and really the stories are mostly self contained regardless of how the ongoing continuity has affected the current status of the crew, but people don't know that without trying the book first. People think if they pick up a random TNG book published in the last few years that it will be constantly referencing events from the past few books without explanation, that a random Star Trek book is like jumping into the Wheel of Time at A Crown of Swords.