I'm strange I know!

I'm on the market for a new vest.
I was browsing and saw something on the Simms G3 Guide vest which I don't know what it is used for.

See in this picture http://www.simmsfishing.com/site/g3_guide_vest_09.html#
the thing above the retractors, the thing with the little holes in it!
What's that?

On the Guide vest they put D-rings (http://www.simmsfishing.com/site/guide_vest_09.html)
What's the difference?