Again, I know what you mean, but that's not the point.
Everyone who uses any undead form was once supposed to make such a trade-off and receive no healing from any positive spells.
But the developers decided to change that. All I'm saying is, with exactly the same logic, it should also be allowed to receive "healing" from repairs when you change your form to undead or elemental (also only 50% like undead from positive spells).
Just because maybe fewer players play Warforged or Bladeforged, this doesn't mean that their unique form of "heals" (repairs) is less important.
I can imagine that part of the "why" for undead forms, is that negative spell damage is often very limited in what it can affect. Thus a trade off was made to help make undead builds more survivable due to the reduced potential of negative DPS.
Problem I see with Warforged, is that It's a really old class in terms of when it was added to DDO. Which, really doesn't help it when most of its racial traits, enhancements and docents don't fit well within todays game. Though despite this, within the tree you have healers friend, which is there to more or less offset your problems with positive healing. That being said, your not changing form. The moment you do, all bets are off, as you no longer are considered a warforged.
Per the PM wiki: "You are considered Undead rather than your original type for the purposes of most effects."
Sure from a point of view this appears unfair. Though the form is a choice, not mandatory. And honestly, what's the benefit of undead form as a warforged? If your so focused on playing a warforged, then play one without a PM form. Odds are, you'll not miss PM at all, and by Epics have better self "repair" than anyone's death-aura.
Edit: My gripes with Warforged are about...
- The Racial tree not allowing a player to select intelligence vs. constitution. Having this option, would allow for Wizards to freely use warforged without gimping their DC's and spell points.
- Warforged armor feats, mucking up Dodge, PRR, and MRR in comparison to other similar non-warforge armors. This has been a long-term issue that the Dev's refuse to address.