I have been a Type I diabetic for the past 15 years, and have had the "pressurized stream of blood" that shot across the room a handful of times when injecting my stomach. Granted, being an insulin dependent diabetic, I have given myself an estimated 32,000 injections, which I seriously doubt a steroid user would ever get anywhere close to.
You've got larger arteries/veins to deal with in the stomach area. The buttocks are fairly light on them, and unless you move close to the center, there's nothing with high enough pressure to spurt.
