After reading this question and answer, I was surprised to learn that most shock pumps use a Schrader valve. My mountain biking days are a distant memory, so I'm not well acquainted with the type of shocks that require a pump. But given that high end bikes (the type of bikes that probably feature this kind of shock) almost certainly come equipped with Presta tubes, why would the shocks require a Schrader?
Schrader valves are stronger, for one. Breaking a weaker, smaller valve that has a (perhaps just in my experience) frustrating attachment mechanism for pumps on a $1,000+ fork would be unacceptable.
Schrader valves have at least one valid disadvantage on a road bicycle: their larger diameter is a deterrent for use because it reduces the strength of the rim significantly on a narrow-rimmed bicycle wheel (the main point), they use a spring that can wear out to hold their own pressure where Presta valves hold their own (ancillary point, if one at all) and are slightly heavier (retroactive justification from the Presta preachers). None of these matter for a shock.
High-end road bikes were designed for one thing: going fast. Their rim material takes an enormous amount of additional stress from the smaller width, higher inflation rates of the tires, and simultaneously have as much weight, material, and spokes taken away as possible to leave a somewhat durable wheel. In this setup, the hole diameter DOES make a sizable chunk out of the material and strength of the rim, and the smaller diameter allows for more performance and smaller width, lighter weight rims, and so is 'the thing' in the higher end models. Only a 6mm diameter hole is drilled vs an 8mm hole for a schrader.
Don't confuse 'costs more' with 'better'. In the mountain bicycle / BMX / downhill / trials / non-road bike world, the high end bikes are not all presta. Most utility bicycles (even expensive ones) are schrader for the convenience. They're more of an irrelevant (performance-wise) selection of what the rider wants on these types of bicycles. This isn't because they're skimping in other areas, but the Schrader vs Presta debate doesn't really matter when the rim is wide enough to compensate for the larger hole that must be drilled.
Also note that Schrader valves are much, much, much more common. They're used in refrigerant systems (both on your fridge in your home and in your vehicle's A/C system), plumbing test ports, pneumatic systems, hydraulic systems, and in many other industrial applications as well. I have never seen a presta valve that is not on a bicycle (so if industry is using them, they're cleverly hiding them everywhere I look). This makes the cost of design, tooling, and testing a much less costly proposition for the manufacturer (and, in the end, the consumer) - by not having to break the trail for using a less common valve in an application it's not been used before.
A fringe benefit of Schraders that may or may not apply in this context is the removable core. When I was a Diesel mechanic the trucks would get ice and dirt lodged in the valve stems, and a simple tool would extract the core, leaving a decent size diameter to expel air, or shove a small screwdriver into to clear debris. Further, if the spring was ever worn, or the seal mechanism not sealing, this core could be replaced without replacing the entire valve stem, and it made depressurizing tires much more tolerable (take the cores out, walk away for five minutes). I couldn't imagine how irritating Presta valves would be. If the seal seat of a presta valve 'wore out', got chipped or otherwise failed on a shock, the whole valve would have to be replaced - which depending on the design, might be a permanent fixture in the shock tubing.
After doing some more reading after my initial question I suspect it's precisely because a lot of those bikes have a presta type valve. Shocks have a much lower volume of air so they require a lot more precise amounts of air, and therefore leakage generally needs to be avoided. They also normally appear to want a higher pressure than you would normally put into a tire. This means that you generally can not use the same pump you would on your fork.
The modern shock pumps tend to have dials for pressure readings, special fittings to prevent any leakage, and can go up to a higher pressure.