The Most Boring Rule
They say a meme is the idea analog to a virus because of how they spread. Some ideas are also like the flu virus; they make a healthy body weak and ache. And just as the flu lives on from host to host, so do some really crappy ideas.
Like “Defenders win ties.”
That might have a place in some well-themed board games, like Shadows Over Camelot where heroes must “be better than” their foes, but in RPG-land, here’s what happens:
Bob: “I swing my sword at the orc’s face! Because, you know, face!”
GM: “The orc flips out of the way! because, you know, his face!”
[There’s a roll, and it ties]
GM: “Nothing happens! I sure am glad we’re playing this game, Bob!”
And now your hopefully interesting action sequence is going to take one (or two, with an exchange system) roll longer to go somewhere.
When you have a simple pass-fail mechanic where nothing else happens secondarily due to the roll, “defenders win ties” preserves the situation, the moment, the status quo. That’s pretty damned weak when we’re playing a game that claims to be about playing out awesome stories and fights and shit. “Defenders win ties” is not awesome.
Why it Works In Board Games
This mechanic often comes up in board games. Why? Because in that frame, it works. Most often, these board games are either Press Your Luck games or games with a tight, active economy. If an RPG models either of those, then “defender wins ties” can turn into some sort of interesting decision point. And that’s good.
In Press Your Luck games, you want to reward the player being able to Press Her Luck, and thus somehow put that some of mechanic in with your game, like the wager mechanic in Houses of the Blooded.
In a game with a tight economy, a tie often means “win if you’re able to spend a resource” or something similar. (So does “I lost but not by much.), This creates the decision: do I spend to overcome this crap? Fate & Cortex+ work like that, where if you roll a tie and you have the resource to spend (Fate Point & relevant aspect; Plot Point and additional, useful dice). I also see this in Technoir, asymmetrically, but rather than explain it I’ll just point you to the free player’s guide.
(That said, in Fate attackers essentially win ties, just that in typical combat that’s a 0-stress attack — which is meaningless. You put some english on that by a weapon bonus from having claws, and then that tie becomes a vicious 3-stress attack.)
Other Things To Try
Roll off on ties
This is a simple way to make something not a tie.
Aggressor wins ties
Wait, you mean a mechanic that rewards action? Nah, it’ll never work…
Players win ties
Here (assuming a game with a GM), at least preserving the moment rewards the player instead of punishing him. Though, you’ll need to come up with a PvP tiebreaker…
Ties mean Something Else Happens
We did this in The Bad Man. When the players tie in PvP, the Mad City interrupts the fight to Make It Worse. That fits our game pretty damned well, as there’s always looming adversity.
Defender Still Wins, But There’s More To It
Maybe the defender wins ties, but you get a +1 forward to your next roll because of an advantage, or maybe the defender has a negative modifier to the next thing rather than a lasting consequence, etc. Something where the situation doesn’t remain static. Or something akin to Don’t Rest Your Head, where success or failure on a roll still tweaks an economy.
In short: if you can’t make the roll interesting somehow mechanically and they can’t buy their way out of a boring tie, don’t let ties lead to boring inaction. Unless you hate freedom.
 As does Void Vultures, though for the first fight last night I had yet to introduce the economy & rules from that. But once that was introduced, people pushed back from times where I, as the Void Master, won the tie. And the game started to sing.
 I rather enjoy the rül about that. But then, I would.