I can confirm this information for the ps3 version, and it works with all weapons, not only with blowpipes.
I was quite surprised that this bug wasn't already known to most people, so I took a quick look at a seraphim of mine and posted my theory in this thread http://darkmatters.org/forums/index.php?showtopic=16444 a few days ago, unfortunatly it hasn't survived the hack.
It seems that the dmg boost you get from the attributes gets bigger the lower the level of the weapon is.
Strange thing is that it only effects the hard dmg rings.
An again here are some numbers from a level 145 seraphim that led me to that explanation:
level 146 vs. level 1 halberd, no hard dmg rings, no dmg increasing stats on them.
level 146 (max. 462 dmg)
max dmg in overwiew: 3815
dmg boost displayed at strength: 1411
level 1 (max. 53 dmg)
max dmg in overview: 1887
dmg boost displayed at strength: 1391
that changes when you use hard dmg rings (in this case 342 hard dmg from rings socketed into the armor):
level 146 (max. 462 dmg)
max dmg in overview: 8611
dmg boost displayed at strength: 3507
level 1 (max. 53 dmg)
dmg in overview: 17507-18…
dmg boost displayed at strength: 15931
I remember Bariel did some tests and saw the same effects with blowpipes.
What wasn't tested was if there's a point where a ring with +x attribute gives more dmg than a hard dmg ring when already having a certain amount of hard dmg rings socketed. As I haven't much time for sacred this week, it would be great if someone could check this.
Hope that was understandable, cause my last english lesson was about 8 years ago.