You have two, seperate issues here.
The fuel bladder/intergral tanks are one issue.
The number of sumps are a second.
Apparently, the reason Cessna now has 13 sumps on the new 172s (I flew Rs for my primary and am quite familar with all 13 of 'em!) is because of lawsuits in the late '60s and primarily in the '70s. Morons ... sorry "pilots," would head out to their bird, hop in, turn the engine over and fly away, never having sumped the fuel tanks. Then - surprise, surprise - when the engine would choke due to water in the line the "pilot" would invaribly bungle the "emergency" landing and in turn he or she would sue Cessna citing that they "had sumped the aircraft" but the "sumps didn't get it all." The lawsuits got so bad that most GA manufacturers quit making small GA aircraft which is why all of us are flying around in old beat up tin cans.
As a precautionary measure the new Cessnas have an insane number of sumps partly as legal protection against would be morons.
The tank/bladder issue is an engeneering/manufacturing measure. Each has it's merits and drawbacks but I'm not sure this change is directly related to the number of sumps or if they even did, infact, change from one storage method to the other.