Michael says he doesn't get why Leica added a 35,50,75,90 to the M line given the digital factor for an M8. Remember Michael, these lenses follow on the introduction of a 28, and a combo 16-18-21 in the last 8 months. So to your point, they have already covered the wide side of the M series quite well. I'd say they both want to sell up the buyers of the M8 who just bought the camera with a 28 and additionally they are l are finally starting to compete with their less expensive lens competition.
Hey I'm delighted they are rapidly developing new lenses regardless. And you know what? I'm going to buy the 75 2.5 for a portrait lens. I sold a 75 1.4 two years ago just before they announced that a digital M could even be made. But a 1.4 was a big heavy lens and I doubt I would use it much with the M8 anyway. My 90 no longer works well as a portrait lens with the 1.3 factor, so for me they will have motivated me to buy a new 75 I might not have purchased in the larger f2.0 size.
Full disclosure, I bought the 28 with a 16-18-21 on order via the 30% discount in the last 4 months. That's on top of already having a 21 2.8, a 35 1.4 a 50 (that I will sell) and the 90 2.8 I already mentioned. Oh, and I sold the two M6's that I never used in the last two years. So Leica has gotten me to purchase over $8,000 in equipment in one year, after not buying any M gear since 1992.
Canon with their so-so lenses, has not gotten me to buy any new lenses since I bought my 1Ds years ago. So I'd say Leica is figuring out my market better than Canon.
Just the thoughts of one shooter, but you asked.
Jack