I haven't played the gruul deck yet, but the orzhov deck is actually fairly reasonable. It's basically just about setting up some kind of incredibly slow clock, while just surviving because the deck is a huge pile of marginal value guys.
The Gruul deck overall is weak but many comments here fail to understand the deck... Those who can't see the mechanics here didn't properly read the decklist.
The Gruul deck is about combat tricks (it's easy to run 12-17 of them) and trample... so many ways to give trample... The combat tricks is pretty much your only form of removal (aside from the 3 burn spells) and you force your opponent into blocking sometimes much more than they need because you can chain 2-3 combat tricks and the game is over. That said, the deck is aggro but not fast or consistent enough, and folds to the many removal heavy control decks in the meta... it's pretty sad to see a murder/unmake/go for the throat fall on your critter after you pump it and Berserk... There's only one Fling in the deck too.
I found the deck fun to play with but it's not a competitive choice at all, it's not fast enough and the meta is based on removal that the Gruul deck folds to.
As for the Orzhov, the theme they tried to play around is slow death via many small drains...
The deck has many removal (Unmake, Pillory of the Sleepless, Vindicate, Damnation) and tends to stick around via lifelink and some drain effect..
But the key here is Zealous Persecution. The meta is filled with 1 toughness that you are going to clear out of the way and the card is mostly used as a combat trick turning your 1/1s into 2/2s and your 2/2s into 3/3s.. killing your opponent's 2/2s.. It's some neat card advantage and it often turns the game over in your favor.
Later on, Bloodgift Demon helps you not to be top decking too much and I found Voracious Hatchling to be more useful than it seems if it's not taken care of right away.. a single Zealous Persecution in your combat phase gives it +3/+3...
I would agree that this deck doesn't have much synergy aside from playing black/white.. some lifelink and removal.. you survive and look for card advantage opportunities... that's how it plays. Zealous Persecution makes the deck.