It's a lot more than an excuse; The simplest "a.b" has to check a lot of places before it gives an answer, and each of these needs its own in-line cache. Indeed, there have been experimental compilers for Python that gave much improved speeds for subsets that drop the ultra dynamic constructs (and usually a lot more dynamism and features to achieve that speed).

And the fact that there are languages as dynamic as Python is not as important as how it is implemented through the language; Lua is about as dynamic as Python, but with effects that are much more local in general. IIRC Mike Pall (of LuaJIT fame) said that Lua was almost optimal for JITting, JS is sort-of-ok if you ignore some things, but Python is beyond hope -- and I tend to think he knows what he's talking about, given that his hobby, one-man-show LuaJIT handily beat all well-funded-with-tens-of-employees JS engines for a very long time (maybe still does).

I wonder how good the SmallTalk JITs really are by today's standards, in the presence of e.g. "become:". The fact that's it is there, and supported, doesn't mean it's in common use, or supported efficiently -- just like JavaScript's "with".