There is huge churn in the world of bicycle standards these days. For most of my years as a cyclist (about 14), things like head tubes, bottom brackets and handlebars were standardized. Head tubes on frames were set up for 1-1/8" head sets. Bottom bracket shells were 1.37" with 24TPI. Bottom brackets themselves were square taper. Handlebar diameters were about 25mm. Now we have all types of integrated headsets and even different diameters top on bottom. When bottom brackets went external, some genius figured out that wasn't such a good idea after all, so now we have multiple integrated bottom bracket standards. There are now two popular handlebar diameters, one creatively named oversized.
I've been pretty much a life-long Shimano devotee. My first bike when I became reacquainted with cycling back in 1996 came with Grip Shift controls. I moved to New England a year later, and every bike since, about 16 bikes in all, has been Shimano equipped.
One thing I really came to like about Shimano was they held the actuation ratio constant among almost everything they sold. Actuation ratio is the ratio between how much the rear derailleur moves vs. how much cable the shifter moves. Until now, Shimano was claimed to have a 2:1 actuation ratio. This means the derailleur moves 2mm for every 1mm the cable moves. I measured this on a bike, and I get something closer to a 1.6:1 ratio. Shimano doesn't publish this anywhere.
A universal actuation ratio is important for me as a hillclimber. This allows me to mix and match road and mountain bike components. As long as the number of shifter clicks matches the number of cogs in back, it will work. I could shift mountain bike XTR derailleurs with road Dura Ace levers or even the other way around if I wanted to be goofy. 8spd, 9spd, 10spd, it didn't matter. Clicks = cogs, it will work. Three of my bikes with road shifters have mountain bike derailleurs on them right now, my hillclimb bike, cross bike and my all-around road training bike. I never need worry if my gearing is suitable for a hundred miler with 20% grades in it.
When Shimano first adopted 10spd road gruppos, it messed things up a little, as if I wanted to "upgrade" my hillclimb bike to 10spd, I didn't have a suitable MTB 10spd cassette to put on back. Sure, folks like IRD made a Shimano compatible 10spd cassette with some pretty big cogs in it, but it weighed a ton of bricks, being stamped steel. It was wait and see if Shimano came out with 10spd drivetrain for off-road use.
Personally, I think 10spd is stupid for road and even stupider for off-road. When MTB drivetrains went from 8spd to 9spd, problems with chainsuck quadrupled and things wore out twice as fast. I really didn't want to see Shimano come out with a 10spd drivetrain, as that probably meant 9spd would go away and my bikes would be left with orphaned drivetrain components. I can only imagine how much more 10spd will cost, how much shorter it will last, and how much less tolerant of mud it will be.
Well, Shimano not only introduced 10spd MTB drivetrains this year, they changed the friggin actuation ratio too! They call the new gruppo Dyna-Sys. This means I will not be able to mate a new 10spd Shimano derailleur to my 10spd road shifter. Shimano reduced the actuation ratio, which means the shifter must move more cable per cog. This also means you cannot backfit any older 9spd stuff with 10spd shifters or derailleurs. You gotta replace the whole deal - shifters, derailleurs and cassette.
I can't really blame Shimano for doing this. To make 10spd work in an off-road environment, they had to make this change. 10spd gear changes with the old actuation ratio would mean little more than a millimeter of cable pull to effect a shift. That is pretty fussy. No idea what they new ratio is. All Shimano says about it is the derailleur uses new "Long Arm" technology, which simply means they put bigger lever arms at the cable/housing attachment points on the derailleur.
SRAM went to a 1:1 actuation ratio in their 10spd off-road stuff, calling it "Exact Actuation." At least they tell us what the ratio is. I've occasionally ridden SRAM drivetrains over the years on rental and borrowed bikes. I've never been very impressed with the shift feel. This is especially true for their road indexing. I haven't tried the newest off-road 10spd shifters yet.
I'm betting Shimano will jump on the 11spd road bandwagon soon. When will this madness end? If Shimano does, I suspect they will roll the new actuation ratio into 11spd. This would bring a little harmony back into the drivetrain realm.