Well, okay: money. (And time, people, resources, but if you have money, you can buy those.)
V8 has a team of brilliant, highly-specialized, highly-experienced (and thus highly-paid) engineers working on it, that have decades of experience (I"m talking individually – collectively it"s more like centuries) in creating high-performance execution engines for dynamic OO languages. They are basically the same people who also created the Sun HotSpot JVM (among many others).
Lars Bak, the lead developer, has been literally working on VMs for 25 years (and all of those VMs have lead up to V8), which is basically his entire (professional) life. Some of the people writing Ruby VMs aren"t even 25 years old.
Are there any Ruby / Python features that are blocking implementation of optimizations (e.g. inline caching) V8 engine has?
Given that at least IronRuby, JRuby, MagLev, MacRuby and Rubinius have either monomorphic (IronRuby) or polymorphic inline caching, the answer is obviously no.
Modern Ruby implementations already do a great deal of optimizations. For example, for certain operations, Rubinius"s
Hash class is faster than YARV"s. Now, this doesn"t sound terribly exciting until you realize that Rubinius"s
Hash class is implemented in 100% pure Ruby, while YARV"s is implemented in 100% hand-optimized C.
So, at least in some cases, Rubinius can generate better code than GCC!
Or this is rather matter of resources put into the V8 project by Google.
Yes. Not just Google. The lineage of V8"s source code is 25 years old now. The people who are working on V8 also created the Self VM (to this day one of the fastest dynamic OO language execution engines ever created), the Animorphic Smalltalk VM (to this day one of the fastest Smalltalk execution engines ever created), the HotSpot JVM (the fastest JVM ever created, probably the fastest VM period) and OOVM (one of the most efficient Smalltalk VMs ever created).
In fact, Lars Bak, the lead developer of V8, worked on every single one of those, plus a few others.