Then they are idiots and should read Rippletoe's other book Practical Programming. You do NOT stay on the same program forever ... especially the starting strength one which is for STARTING OUT ie beginners. Cripes I think the book even says you will probably be on it for 6-12 months, NOT for 2-3 years.
5x5 I have never found hard, not even when using my 5RM on EVERY set. I kid you not. In my stupid youth before I realised you were not meant to use your rep maximum on every set (before internet, before books, when there were only dodgy crap magazines full of lies, and I could hardly afford them anyway).
So if I don't find 5x5 hard and other people do what does that tell you? It tells you everyone is different and suited to different things, and also, this changes over time.
The rule usually is
- do what is hard, but not too hard
- keep doing it until it is easy, or you're exhausted
- do something else (harder, or take a rest)
I am currently using 5x5 as part of my RE work in a westside template (that I made) ...
Week one: 5x5 with weight X
Week two: 5x6 with weight X (same weight - but one more rep per set)
Week three: 5x5 with weight X + 5% (or 10% or whatever)
Week four: 5x6 with weight X + 5%
Adding one extra rep per set with same weight is really really fatiguing those fibers nicely. Rather than adding weight, which I am doing on the ME day.
Similarly I am doing the same with 3x8 and then 3x10 (adding 2 reps to that set).