I try and think of Gravity as the curvature of spce time - a field effect, versus particles transfering energy (Gravitons or Higgs Boson in a Higgs field) moving through the field.
In this regard it means not forces moving within the field, but the topology of the field can proprogate at some rate as being defined by say the "tension" of the field. This means I think of the limit of light's speed in our field as intellectually the equivalent to say plucking on a guitar string lightly or hard and wondering why the string moves at a certain frequency. Light propogates at the "tension" of the field.
So without defining what sets the "tension" of the field that is our reality - our Universe (and the speed of light being a constant I seem to remember from 2nd year Uni phyics can be derived from Maxwell's equations alone; with some tricky maths) one can intuit why gravity's rate of propogation could be the same as lights.
Now from (unreliable) memory about 7 years ago physicists (99.999%) of them believed the results of a deep space observation (Jupiter vs quasars
http://www.jupiterscientific.org/sciinfo/sog.html) to confirm gravity changes in a field at the speed of light (those same 2 folk that say its not gravity - its electromagnetic force - disagreed with the finding).
By the way the first link on WIKI did some complex maths, but right at the start they said the Sun is 8.3 light minutes away (it changes Jan its less, July its at maximum distance) but it said the Sun's true position is 20 arc seconds East of where it appears. The Sun moves 15 arc seconds a second through our sky (or 15 arc minutes a minute) - why eclipses only last 3-4 minutes - the moon is 30 arc minutes in apparent diameter - so the Sun by my figures is 2 degrees East - not 20 arc seconds - of where it appears.
Cheers,
Matt