Ork boyz should be strength 4

[ElCheezus]

On S4: S4 is the magic number where you can glance vehicles without equipment. That, plus all the other "balance" and "points values" arguments.
Ork boys, unlike guard blobs, seem to be aimed at winning assaults in short order instead of over time, so their power is front-loaded, with only the PK keeping them lethal through multiple turns. Having FC and such a low save supports this. If orks can't manage to get the enemy crippled in one assault, they're not meant to win the long fight.

On I +1 on Waaagh: Getting fleet and having so many attacks and spare wounds already gives Orks a huge advantage in assault, even if they go second. Even losing a bunch of models before swinging, they still have tons of attacks, and aren't likely to lose the PK. Having fleet already gives a huge advantage over other assault units: a good player can work the assault range to almost guarantee getting the charge. Against guard blobs, this is bad enough, but at an additional initiative, it would be flat-out no contest.

On fearless being a liability: If you couldn't tell, I play guard. I don't usually blob, and prefer vets. I would love to have fearless. Extra wounds vs being swept and losing everything: easy choice. True, fearless isn't quite as good as stubborn and a decent LD, but it's way better than nothing, especially with such a low Initiative.

[RocketRollRebel]

Yes they should, but for balance reasons they aren't.

nailed it.

[Melissia]

I forget, do Space Marine's power armor also add Strength? Been a while...I really need to start playing DH again.

All power armor adds strength, and the same amount of strength as well (civilian, inquisitor, sororitas, astartes all add +20 strength). Except for a specific variant called Light Power Armor which adds I think +10 at most, which also is roughly equivalent to Carapace armor in protection.

No human military forces use light power armor however.