Reach out and touch...

[Kinneus]

The purpose of the Reach weapon is to keep non-OoE foes away from the Avenger, so he can get full utility of hie OoE, right?

If Reach weapons cannot strike adjacent targets (I don't know- haven't even looked at the Reach rules since I'm playing a Warlock), then a Reach-weapon equipped Avenger needs a way to deal damage up close while still using the Reach weapon to keep others at bay. Monk's FoB would seem to be an answer: either unarmed or with the Reach weapon, Monk attacks generally ignore weapon properties, so a Monk FoB attack with a reach weapon would still work close in.

I still don't understand how a Reach weapon would keep anyone "at bay." Are you perhaps confusing Reach with Threatening Reach?

All a Reach weapon does is let you attack something 2 squares away, in addition to being able to attack something adjacent to you. That's it.

Also, as others said, Monk's Flurry of Blows is auto-damage. Melee or implement doesn't factor into it at all. If you hit with an attack on your turn, then you can use FoB to deal damage to a creature adjacent to you. And even if Reach weapons prevented you from attacking adjacent targets (just to be clear: they don't) then FoB still wouldn't be 'the answer' for Avengers. With a monk multiclass, you can only do FoB once per encounter. And you still need to hit with an attack first before you can trigger it.

 

[Nullzone]

The purpose of the Reach weapon is to keep non-OoE foes away from the Avenger, so he can get full utility of hie OoE, right?

If Reach weapons cannot strike adjacent targets (I don't know- haven't even looked at the Reach rules since I'm playing a Warlock), then a Reach-weapon equipped Avenger needs a way to deal damage up close while still using the Reach weapon to keep others at bay. Monk's FoB would seem to be an answer: either unarmed or with the Reach weapon, Monk attacks generally ignore weapon properties, so a Monk FoB attack with a reach weapon would still work close in.

if they can strike adjacent targets, then there is no issue with using a Reach weapon at all: use the Reach property against those you wish to keep at bay, don't use it against your OoE foe.

Reach weapons can attack up to 2 squares away, they aren't limited to just that second square.

The reason reach weapons are an 'issue' for Avenger is that reach weapons often sacrifice other good properties in order to achieve their reachiness. While it is true you can use a reach weapon adjacent and thus still make use of Oath of Enmity, the entire advantage of a reach weapon is that extra square of attack range. It's squandered on the class, so instead of taking something like a Fullblade or an Executioner's Axe to maximize damage you're spending your feats on a Greatspear (or simply attacking with a less than ideal weapon in a Gouge or Longspear).