Baxter:
The difference is that the C441 was designed and type certified under a different set of rules than the Dash series.
Most new designs certified under FAR 23 have a life limit already noted in their MM.
These life limits can be changed by the manufacturer as operational experiance is gained.
An example is the Cirrus; it's initial life limit was 4,000 hours, now all Cirrus have a life limit of 12,000 hours and I understand that is about to be extended to 18,000 hours.
Not that 18,000 hours is a 'throw-away' event. Cirrus plan to have an airframe inspection process to extend beyond that time.
Therefore, either Cessna or another company may develop an airframe mod or inspection schedule to extend the C441 beyond 22,500 hours.
The Piper Trauma-Hawk has an 11,000 hour life. But a company in the USA got an STC mod approved to extend beyond that.