In my cynical opinion these are probably not mistakes and somebody has possibly hidden some documents. As for the 25% that is just an arbitrary number imo and the real number is quite possibly much higher.
A technique the banks are using right now with their mortgages is to lend the money over a much longer period say 30 years now instead of 20. This produces a crap load of more interest paid to the banks. That may not be the worst but at the low interest rates being charged by the banks you would think they are doing a good thing until you think about what another ten years means. What happens when the rates start to rise say back to 8%. That extra ten years is going to reap a motza of extra interest for the banks. The banks are in it for the long haul and Im sure they understand the whole concept. Low rates just make the term longer and get much more in the long run and given that most of the interest is paid in the first 60% of the time they are way ahead.
