I would say it is still important and will be for the foreseeable future. Hydraulic power provides the most positive mechanical advantage possible. Because of the incompressible nature of a fluid, air is not an option. Electric circuits require an electro/mechanical interface not required by hydraulics, hence more reliability. The fail-safe requirements of aerospace requires a positive power transfer not available by any other means.

For years, well at least since 1988, I have been saying something similar by wondering why Hydraulics and Pneumatic (Fluid Power) has always been without TRAINED/DEDICATED persons except for the Manufacturers, Distributors and Sales persons. TRAINED/DEDICATED Electric and Mechanical persons have been making inroads into the Fluid Power field on a daily basis since they understand the operation and limitation of their fields equipment and know how to best apply it.

However, Fluid Power has muddled along with attempting to be an add on to the Mechanical Engineers profession. The sad part is an ME only gets 1 or 2 semesters on the subject and may be in the field several years before they are asked to use the meager information they left school with. However, some have had the opportunity to attend a 1-2 week Hydraulic or Pneumatic class put on by a Fluid Power Manufacturer and again have little or no need to apply the learning until it is lost in their memory banks. Should not be that way, BUT, from the feedback I've received over the years there is No Change in sight.

Needless to say sytems like some 2,500 Ton presses in my area will always be Hydraulic since their operation does not readilly lend itself to Mechanical or Electrical methods. At the same time the proocess they perform has been changed to Electro-Mechanical in severl new facilities I have seen. The products end results is not as good but the simplicity and cost of of the process outweighs the 5-10% reduction in lost product output.

Just some thoughts.

"So is the aerospace market for hydraulics all that important?" The saw mill industry relies on hydraulics to move logs and saws with precision. When a log is rolled on to a carriage there is a lot of shock that destroys electro-mechanical actuators. Presses are another application where hydraulics rule. A hydraulic press requires little if any power to apply forces whereas an electric motor must have current flowing through the armature to provide torque. In some cases the motor is too heavy or big to be mounted close to the actuator. Each electric motor must be sized for the peak load. A well designed HPU only needs to be designed to supply the average power plus a little more. The peak power requirements can be met with accumulators that are charged in period of inactivity. This point is key but also makes it pretty clear where electric motors have an advantage of hydraulics. If the load is continuous like moving a conveyor the an electric motor has a decided advantage. My company sells hydraulic motion controllers for industrial hydraulic applications. The applications are many. We have specialized in hydraulic control but we realize that hydraulics is just another way of getting power from one place to another and isn't any more or less special than ball screws, rack and pinions, gears, drive shafts, chains, belts, etc. For instance a belt drive is similar to a hydraulic system in that the mass/load is attached by two springs. The same control problems exist. Each way of getting power from one place to another has its own pluses and minuses depending on the application