Yes, of course all clients are individuals and therapy - if it's any good - will end up being tailored to their needs. But:

1) as pointed out by a number of posters, therapy does need to come with some warnings. Clients with unrealistic expectations are going to struggle more. It's simply good practice.

2) statistics does not mean hard and fast numbers. One can easily say, "the average amount of time a client [not talking about the ones who don't come to a second appointment, no one ever was] spends in therapy is 4 years, but your mileage may vary." This at least gives a time frame to a client.

The more transparent the process and the therapist, the better it will go, and with any luck the less heartbreak clients might experience.