Probably both looks and price points. At $150 and much uglier than the $99 E2's, the E1's seems to be just missing the market for consumer purchases. I can't say if it's really a better phone than the E2, since I never heard it myself.
The E1 has been around a long time as well, but it's always been marketed toward pro-musicians, only recently (with the E2 and the E5) it was also marketed towards consumer as well. The E2 is definitely a consumer earphone, and the E5 is a combination consumer/professional product.
It's easy to say that the ER-4 is better than the E2, but it's hard to justify the ratio of the price different alongside the performance difference. So it might be even harder to say the extra cost of the ER-4 is worth it over the E1... but again, I haven't heard the E1, so I don't know.
To answer your question, the E2 has a "filter"-like thing, except it's not like the Ety filter. The tube size of the E2 is pretty large, so they have this "sticker" filter that gets stuck on the end of the tube, all the wax should stick to just the filter (if any) and never get inside. I never had a problem with having to remove the wax from the E2.
The E1 and E5 does not have any sort of filter, the tubing is small enough that it should not be a problem. They do give you a tool to remove earwax should any ever get inside. I have never had to deal with any earwax removal (other than cleaning the sleeves) since I've got the E5 about 5 months ago now..
Personally, I've never understand why filter on the Ety's were needed, but I didn't have the Ety's long enough to have ear wax build-up on them. Perhaps the ear-wax somehow makes it into the Ety's tubing much easier (and there's plenty of people that had to replace them, so I'm sure it does happen)...