I don't know Where you got that idea ferron. There are alot more moves that are higher BP and higher effect, Thunder, Muddy Water, Sacred Fire to name but a few.
I think it's clear that everyone wants an effect that is going to occur fairly frequently. Since Gamefreak seems to take 30% as the bar for a plethora of Attack + High Chance of Side Effect moves, here's a list of Smogon's moves sorted by % chance of effect occurring.
Since we want a reliable STAB, and the best Physical Ghost STAB, Shadow Claw is 70BP, I'm only including moves of 70BP and over.
Most people want a reasonably accurate move too so I'll also exclude moves of less than 85% accuracy.
Name Power Accuracy Side Effect
Luster Purge 70 100% 5 50% chance to lower SpD 1 stage.
Mist Ball 70 100% 5 50% chance to lower SpA 1 stage.
Crush Claw 75 95% 10 50% chance to lower Def 1 stage.
Sacred Fire 100 95% 5 50% chance to burn. Thaws the user.
Seed Flare 120 85% 5 40% chance to lower SpD 2 stages.
Poison Jab 80 100% 20 30% chance to poison.
Sludge Bomb 90 100% 10 30% chance to poison.
Body Slam 85 100% 15 30% chance to paralyze.
Discharge 80 100% 15 30% chance to paralyze.
Muddy Water 95 85% 10 30% chance to lower accuracy 1 stage.
Air Slash 75 95% 20 30% chance to flinch.
Headbutt 70 100% 15 30% chance to flinch.
Iron Head 80 100% 15 30% chance to flinch.
Rock Slide 75 90% 10 30% chance to flinch.
Lava Plume 80 100% 15 30% chance to burn.
I don't know if this will help or if most of you have already looked for yourselves. Either way it might provoke some more discussion of the balance between power, accuracy and % chance of side effect occurring.