Pw

[Ghebert]

Is that because the loyalty counters are the cost of that ability?

Precisely.  DS says:
"If an effect would place one or more counters on a permanent you control, it places twice that many of those counters on that permanent instead"

Adding counters by activating a PW's ability is a cost, not an effect.

Yep. It's considered an activated ability.

[BlackJester]

Costs are not effects.

[Keyeto]

Ahh alright. Thanks for clearing that up BJ!

[BlackJester]

Ahh alright. Thanks for clearing that up BJ!

You're welcome.  It's what I do.