Since there aren't many players in the Ruby language space, this is probably not an issue, and it's all down to how good a job the standard writers do. (Basically, I understand it's basically only matz who determines what is and isn't Ruby.)
What this should buy the community: protection from future vendor/implementation fragmentation. (But only if it's a strong standard with "teeth.")
* The super-important MRI/YARV team
* The mruby team
* The super-important MacRuby team
* The IronRuby team, to the extent it still exists
* The super-important JRuby team
* The super-important Rubinius team
Other languages also have multiple implementations, but they aren't really in viable competition with each other like they are in Ruby (a good thing for Ruby).
Jython vs CPython vs PyPy vs Stackless Python vs IronPython
HotSpot vs OpenJDK vs Dalvik vs GNU Classpath (libraries only) vs Jazelle VM, etc
There is some argument as to which feedback into the language and which are "pure" implementations but I think the point still holds, many languages are pulled in many directions by either their runtime or their compiler.
The argument for Java is clearer and it's a well known case of the interaction of multiple implementors, and thus it has an standardization process.
MRI, JRuby, and Rubinius were or are running significant populations of web apps. I wasn't aware that MacRuby was widely used for other than building apps on OS X.
Contrast this with Smalltalk, which at one point simultaneously had VisualWorks, Smalltalk Agents, Digitalk VSE (merged with other vendor), Smalltalk MT, IBM VisualAge Smalltalk, ObjectStudio, Smalltalk/X, Dolphin Smalltalk, and Squeak, all of which were actively being used to build or maintain desktop apps, and all but two of which were running on Windows. On top of that, there were significant semantic and syntactic differences between all of them, which make the differences between Ruby implementations seem quite minor. (Really messy and fundamental differences like namespaces and what does one expect Dictionaries to return when you insert something?)
Back in 1999 or so, most of the Smalltalk implementations were commercial, and many of the companies had no incentive to interoperate and some incentive not to. In contrast, I think there's more incentive to interoperate and avoid language forks for the Ruby community.
Also, if one considers the population of Smalltalk devs back then compared to Ruby devs today, then no, I wouldn't say anomalously many per capita. BASIC and Forth seem to be in a different league for number of implementations. One would have to do some digging, but it might be argued that Ruby has relatively few implementations even for its relative age.
* GNU (gcc)
* Visual Studio (mscl)
* Intel (icc)
* ARM (armcc)
* TI (cl6x)
* LLVM (clang)
Having used all of these compilers (plus more), all implementing the same language, I would say that there is much more meaningful competition in the C space.
Having a standard is a good way to allow better competition, but it does depend on how good the standard actually is.