Have 2005 Grand Cherokee, had oil changed as usual every 3000 miles they recommended a fuel induction service, rear differential service and power steering flush are these needed or what vehicle has 51000 miles, 90 % in town driving.

The fuel injection service will help to maintain your fuel economy, however it will not kill your vehicle to put it off. the rear Diff service is pretty essential. your differential has tightly meshed gears that require proper lubrication to maintain viable operation. not performing this service will leave fluid in the diff that no longer properly lubricates the gears, thus leading to premature wear. the power steering fluid is a hydraulic fluid. if it gets contaminated, it will cause the power steering pump to wear prematurely. it is not a good idea to forgo this service either.

Most of that is not scheduled maintenance items. I would have your fuel filter replaced, if not done yet, it should be done every 20,000 miles. Alot of these places get a small commission for selling added services. I would go by the maintenance schedule in your owners manual.

Fuel filter is a 100k plus interval item.
Fuel filter is built into the fuel pump in the gas tank.
Here is a video describing the process to remove and change the pump assembly.
https://www.youtube.com/watch?v=9gmRG5ECodo