After 29 years in the industry I can say Maintenance is 60-80% of total cost. Development is at most 20%. But most companies today don't seem to acknowledge that they put the most focus on fast development and set due dates without proper estimation. This forces developers to dump and go, which only makes the maintenance harder. So what do the execs do as a result? They throw away all in-house software and buy 3rd party stuff. Then the nightmare of system integration happens and maybe 4 or 5 years later they will kind-of, sort-of get it all working but the cost to do that is exponentially higher than spending the time up front and doing it right the first time. In the meantime all the seasoned old timers hang up their hats and a new breed of young bucks fly in with the attitude of "we can fix anything". And that, my friend is what they'll be doing for a long time.
This is why Agile eventually won me over because waterfall just doesn't work in software. Never has and never will. It's all about smaller working iterations and parts development. Just like Henry Ford showed us in 1900...
