IO540,
I accept regulations are open to interpretation but try as I can, there is no way I can interpret 91.175(a) in the same way you do
You do bring up some interesting questions about Class G. Class G is not some lawless zone where the regs don't apply, you just don't need a clearance to fly in class G, IFR rules still apply.
FAA certificate holders are required to immediately climb to MEA which is specified in 91.177 and 91.179. Thats going to be 1000ft above anything within 5 miles, and also teh hemispherical rules apply. Basically no lower than 2000MSL or 3000MSL depending on your course.
You ask when the approach starts. For an airport with no IAP I would say the approach starts when you leave the MEA. What are the requirements? In Class G you need to have VFR minima (91.169(c)(2) ).
VFR mimima in Class G are
<=1200 AGL
during day clear of cloud and 1 miles vis; night 3 miles vis and 500/1000/2000 (91.155).
>=1200 AGL
day 1 miles vis and 500/1000/2000
night 3 miles and 500/1000/2000
This says to me that pilots relying solely on their FAA certicate to fly IFR cannot descend below MEA in class G unless you are clear of clouds by 500/1000/2000 ft.
Sec. 91.177
Minimum altitudes for IFR operations.
(a) Operation of aircraft at minimum altitudes. Except when necessary for takeoff or landing, no person may operate an aircraft under IFR below
...
..
(ii) .... an altitude of 1,000 feet above the highest obstacle within a horizontal distance of 4 nautical miles from the course to be flown.
Sec. 91.179
IFR cruising altitude or flight level.
(b) In uncontrolled airspace. Except while in a holding pattern of 2 minutes or less or while turning, each person operating an aircraft under IFR in level cruising flight in uncontrolled airspace shall maintain an appropriate altitude as follows:
(1) When operating below 18,000 feet MSL and--
(i) On a magnetic course of zero degrees through 179 degrees, any odd thousand foot MSL altitude (such as 3,000, 5,000, or 7,000); or
(ii) On a magnetic course of 180 degrees through 359 degrees, any even thousand foot MSL altitude (such as 2,000, 4,000, or 6,000).
91.169(c)(2)
(2) If no instrument approach procedure has been published in part 97 of this chapter and no special instrument approach procedure has been issued by the Administrator to the operator, for the alternate airport, the ceiling and visibility minima are those allowing descent from the MEA, approach, and landing under basic VFR.
However I agree that you don't need any minima to depart in class G. However FAA certificate holders might be interested in ....
Careless Reckless (PDF)
So that's my interpretation. Over to you