OK, I may have dozed off in the last few posts...
Are high runes rare? Of course.
Is finding them as rare as stated previously? No.
If you just hurry and kill the Countess or Mephisto or Pindle... you'll find that you have a terrible chance of finding high runes. Sure some of these have the best possible rune drops, but what's the use if you only kill them once every couple minutes?
If you go to an area with lots of monsters, and you can kill groups every few seconds, that's so many more chances to find a high rune. I do a few Countess runs now and then (usually to find Amns and Shaels) and never teleport. I walk and kill. And although the best the Countess has ever given me is Ko, I've found 2 Guls and a Vex on the way.
As mentioned before, hell cows is a great place as well. That's because with quite a few character builds, you can clear hundreds of cows in the same time it takes to run and kill the Countess.
That only saves you time, it doesn't alter the drop rates or drop rarities, so it is as rare.
You point is a good one, I'll give you that, because you will find runes much easier just by going through Hell and killing things. Almost every enemy on Hell has a chance of dropping a Zod for instance, and the fact that the highest drop rate is SO low makes the difference between drop rates, from best to worst, rather negligible. Because of that, the difference between fighting the Countess over and over and fighting in the Cow level, independent of the time it takes, is rather the same. Therefore, like you said, when you fight in the Cow level, it's practically like fighting 200 Countess' in terms of the drop rates of runes.
Nevertheless, though, I still reiterate the statistics of the drop rate of the Zod rune:
1 in 15,360,933.
And that's the BEST drop rate, it goes down hill from there.
Fighting Cows will no doubt be better than fighting the Countess over and over, not to mention extra XP and not as boring, but you've still got to kill over 15 million cows, on AVERAGE, in order to get yourself a Zod rune.
I think the numbers speak for themselves.