I hadn't thought about it, but that is interesting. Of course the E before R is going to sound like the R, but the other two are different as well, with the middle one being pronounced like a long A sound.
"Emil Jellinek, an Austrian automobile entrepreneur who worked with Daimler-Motoren-Gesellschaft, created the trademark in 1902, naming the 1901 Mercedes 35 hp after his daughter Mercedes Jellinek."
I suppose that the "different" e's occur in American English?
One could argue that it is also the case in the original German, but the difference between the first and third e is not that strong and depends on the dialect / origin of the speaker. Jellinek's daughter was officially called Mercédès. The accents tell how it is supposed to be pronounced :-)
It is a strange nature of the English language that when the letter E is followed by a letter R, the letter E is not really pronounced. There is one mere exception I can think of.
All the other vowels are pronounced such as: Mantle, Miracle, Mortuary, Mural.
My French Canadian friend cannot say wasps. Whenever she tries, it comes out as wops. Hilarious to watch her try, but I wouldn't recommend she try it in little Italy.