Here's the thing though, blood's self heals, as a tank, heavily depend on death strike + two diseases for an effective 15% heal (with improved death strike). Everything else for a blood tank tank is a cooldown, which means we're not using it cyclically. We're holding onto those for the times when we either know things are about to get ugly... or they already HAVE gotten ugly. Like Rune Tap.... with a 1 min cooldown when fully specced.... it's not like we're just popping it every few seconds to heal ourselves. We hold onto that as an "oh shit" button. Now, a good tank may try to keep a rhythm going with our death strike to have it delivered evenly. Even then, a tank still relies on the heals from our healer to keep us going for the long haul.
And your statement tells me that you don't understand the blood tank. Death strike require two runes PLUS at least one disease to get any heals out of it. And we don't get any healing rom damage delivered because we're walking around in frost spec for the threat. Runes aren't always available to us. Again.... some of us try to establish a rhythm so that we HAVE some runes available and on tap when needed. But what happens if we have to throw down a death and decay to grab agg on adds? Oops. There goes our free heals.
The way you say it..... "on demand".... makes it sound like there's not a price to be paid for our ability to heal ourselves. Our ability to heal ourselves.... or even our cooldowns.... are all tied to a resource that has a cooldown itself..... runes. That's like saying a healer can heal indefinitely. We have to make choices.... do I hold back on using my runes offensively just in case I need a DnD or Rune Tap or Pestilence so I can keep my diseases up? Do I use my rune power for rune strike for threat?... or do I save it for popping IBF or AMS?
On the good side, we're not like paladins who "could" bottom out on mana and be in a bad spot. We're also not like warriors that need to build up rage to get rolling. The rune system is a great system, so long as the demands on it are not over it's ability to refresh itself.
As for the blood tank in Ulduar.... I'm not certain what was the situation there. But, judging from your remarks, I'm hesitant to throw them under the bus yet for failing to use cooldowns/mitigation tools correctly. Then again, I don't get pissy with my healers. I ask them what I can do to adjust to what they're experiencing.
EDIT: Also, don't forget, we're more like bear tanks in that we don't have shields or a block mechanic, so a blood tank may "feel" squishy compared to a pally or warrior.
On the plus side.... we HAVE damage mit tools the bear tank doesn't have, so we can counter when we know big hits are inbound.