Is the difference that drastic?

Short version: Yes.

Long version: Writing quality can be meaningfully compared along many axes. There are mechanical axes, like correct grammar usage, clarity of expression, precision, succinctness, and readability, all of which I found to be problems (to varying degrees) with this post. These are all (relatively) easy to improve by proof-reading, making multiple drafts, and/or asking others for editing help. Wei Dai's post performs well by all of those measurements.

There are also content axes, like originality, rigor, cleverness, evidentiary support, and usefulness. Hacking the CEV for Fun and Profit does pretty well by these measures, too. This post is a little better with content than it is with mechanics, but poor mechanics obscure content and dilute its weight, so I suspect that the points you were trying to make were underevalued, though not drastically so. Fixing up content is harder than fixing up mechanics; for some ideas, it is impossible. After all, some ideas are just wrong or useless (though this is usually far from obvious).

One writing technique I like and don't use enough: come up with lots of ideas and only explore the most promising ones. Or, as it is written in the Book of Yudkowsky, hold off on proposing solutions.

Err... 33 now. But that is because the content is very compelling. Posts pointing out why CEV<Humanity> is quite possibly a bad thing would have to be quite poor to get a downvote from me. It is a subject that is obvious but avoided.

I voted up your post even in its earlier revisions.

However, Wei Da's is far more novel and entertaining. I would have voted it up 3 times if I could :)

These are all questions I (and most thinking people, have considered before): "Would it be better not to exist at all, if existence is mostly suffering?" ("To be, or not to be?"). "If a deist-type god (not intervening after creation) created this universe and all its rules that imply the suffering we observe, was that a moral act?" "How much pleasure (and for how long) does it take to make it worth some amount of suffering?"

If there was much beyond that in your post, I may have missed it.