method access vs variable access

code.rb

require 'benchmark'

def a_method
 10
end
a_var = 10

Benchmark.bm do |x|
  x.report("variable access") do
    for i in 0..200000000 do
      a_var
    end
  end
  x.report("method access") do
    for i in 0..200000000 do
      a_method
    end
  end
end

jruby.txt

variable access
      user     system      total        real
  7.045000   0.000000   7.045000 (  6.791000)
method access
      user     system      total        real
 14.328000   0.000000  14.328000 ( 14.328000)

macruby.txt

variable access
      user     system      total        real
  6.630000   0.010000   6.640000 (  6.630245)
method access
      user     system      total        real
 15.790000   0.000000  15.790000 ( 15.792764)

ruby-1.8.7.txt

variable access
      user     system      total        real
 16.370000   0.000000  16.370000 ( 16.374627)
method access
      user     system      total        real
 33.900000   0.010000  33.910000 ( 33.912025)

ruby-1.9.2-p180.txt

# using rvm 1.9.2-p180

variable access
      user     system      total        real
 13.800000   0.030000  13.830000 ( 13.896888)
method access
      user     system      total        real
 22.180000   0.060000  22.240000 ( 22.345057)