Not to say that the DM should go way out of his way to avoid PC death, but higher EL encounters most of the time will cause this eventually, regardless of player decisions and PC design.
I do see where a lesser number of higher EL encounters can avoid grind or the perception of grind more than a greater number of lower EL encounters, I just also see that there are pros and cons with the approach.
Hmm so far I'm yet to have a PC die as a result of doing this, and I find that using "Hard Encounters" works very well.
What I have instead is less "grinding" through dozens of encounters to get through an adventure, and more time doing the interesting fights. In describing the plot of the adventure I can add in the PCs defeating weaker monsters, or replace that part of exploring the dungeon with a skill challenge (what I'm about to do with Rescue at Rivenroar).
This means that all the combats matter, and the PCs need to think about what they are doing in each one more, and that instead of taking 5 or 6 sessions to get through a dungeon it takes 1 or 2 and the most important thing - the plot - is upheld.
The thing you need to be careful of when using Hard encounters is the Monster level, don't push that up to much or you will end up with problems.
Here's some example encounters (just the monsters) for 3x4th level PCs (a Paladin, a Fighter, and a Wizard)
Encounter -1 The encounter the players rated the toughest. (Because they were trying to conserve Daily powers)
2 Wyrm-Wisp (4th level skirmisher - refluffed and made cold based)
1 Orc Witch Doctor (2nd level Controler)
2 Orog Militants (3rd level Soldier)
Encounter -2 The easiest encoutner. (Wizard cast Flaming Sphere)
1 Cave Troll (level 7 Brute)
10 Orc Drudges (level 4 Minion)
The troll blocked a bridge over a stream the PCs needed cross that was frozen over by a thin layer of ice. So it was the Troll or the Ice & the Troll. The Drudges attacked in 3 waves (3,4,3) and the wizard had fun blasting them away while the Defenders tied up the troll.
Encounter - 3 The last encounter where the PCs got to use what they learnt in encoutner 1 about the Wyrm-Wisps to make better choices in this one.
1 Young Blazewyrm (level 4 Elite Brute - refluffed and made cold based)
2 Wyrm-Wisp (4th level skirmisher - refluffed and made cold based)
6 Orc Drudges (level 4 Minion) widely spaced initially making the wizard able to get only 2 at once.
Each one of the encoutners rates as hard, but none of them were terribly over the top for the party, and in different ways each of them let each character have "cool" moments (the Paladin being grabbed by the troll and marking it so when he was used as a club the troll got hurt being a fav..) each encounter had "gorramit" moments as well keeping the players on the edge of their seats and the possibility they might have to run away in mind.
By the time the final encounter resolved for the night all the party's daily resources were exhausted (except Surges and these were low) and they were high fiving over killing their second Dragon, and the campaign plot had been moved forward with lots of forshadowing of the next adventure.
The alternative to this was to basically add at least 2 more encounters, which would have meant 2 sessions worth of game for the same net effect. Each additional encounter means its more likely to fall into "grindspace" because you just end up fighting more encounters that are essentially the same for little reward. Each encounter might be challenging but after a while it gets to be "another group of X" or you start tossing plot out the window and just putting monsters in to be interesting (the sin Rescue at Rivenroar suffers from). The important thing is to mix up the level of difficulty of the encounters, with WotC's recomendation for "Hard" being the general target range, with a few "Standard" encounters and the very occasional "Very Hard"
The best way to make "hard" encounters is to mix things up; monsters faught, terrain faught over etc etc... (see the rest of the thread really)