Jona, your point is well argued. However, there are currently multiple ways to successfully gear a destruction warlock due to the variability of fights that one will encounter. A lot of gearing a destruction warlock is about playstyle.
http://www.wowarmory.com/character-s...moore&n=Gwills
(Please note Gwills usually does not run with Embrace of the Spider, he must have traded it in for a particular fight.)
Please note that Gwills has 217 haste rating and generally runs with one haste proc trinket. He is one of the top three (horde side) warlocks on my server, one of the most populated servers in the world. Also take note of his 592 crit rating. This works for him for two reasons.
His spells hit hard. Many theorycrafters for warlocks say they can't tell much of a difference between 20% crit and 23% crit in a 25 man group. While in a 25 man raid, you will stop crit a great deal with 20% crit rating, there is indeed a clear and much more reliable chance to crit with 23% chance.
He doesn't have to Life Tap very often. The more haste you have, the faster you cast spells, the faster you run out of mana. The 475 spirit that Gwills receives from his gear are a large boost to the mana gained from his Life Tap (1 spirit = 3 more mana via Life Tap) and a nice chunk of that becomes spell power via Fel Armor (and 20% more with Glyph of Life Tap). With less spirit, you have to Life Tap more and stop attacking the boss to do so.
http://www.wowarmory.com/character-s...moore&n=Cuarto
Personally, I don't like trinkets with haste procs. They throw off my Life Tap timings because I lose mana more quickly than I was before the boost to casting speed. For this reason, I much prefer trinkets with spell power procs (the Conflagrate crits when over 4000 spell power, I must admit, are fun to watch). Ideally, I try to remain as close to 15% haste as possible without going over or throwing off my gear just for some haste boost.
Why 15%? I assume that I run 25 mans with a casting shammy who will have Wrath of Air totem (5% casting speed boost) to put my haste at 20%. When Backdraft procs, my casting speed is increased by 30%, to 50% total, and when Bloodlust is popped, my casting speed also reaches 50% total haste, and I see no reason to go over 50% casting speed. Especially because GCD spells (Life Tap, Soulshatter, Curse of Doom, Curse of Affliction, Conflagrate) receive no further benefit past 50%. Therefore, in my opinion, haste significantly loses its worth after 491 haste rating (with Wrath of Air).
I don't mind putting in a green or purple gem with spirit because of the extra mana from Life Tap, and extra spell power via Fel Armor and Life Tap glyph, and I will do so for any socket bonus besides a stamina or intellect one.
I like to stay between 21 and 22% crit so that raid buffed (with Boomkin) I will be just barely over 33% crit, but when I get gear with more crit I won't complain. In both red and yellow sockets I like to gem for crit/sp gems because I DO need more crit. I'm not happy with my current uptime of Pyroclasm. Instead of doing a +20 crit gem and a +23 spell power gem, I like the two +10 crit +12 spell power gems (<3 the 1 extra spell power).