Gear Inches and Different Bikes?

Whenever there is mention of a bicycle's gearing, inevitably we bring up gear inches. And when there is a question of what gearing is best on a new bicycle, someone will suggest to calculate the gear inches on a bike the person is already comfortable with and use that as a template. But here is the thing: While I known how to calculate gear inches, I've been finding this mostly useless when setting up a new bike - because, in my understanding, gear inches are bike-specific. In other words, the same gear inches don't feel the same on different bikes. What am I missing or misunderstanding here? 

To quickly summarise for those new to the concept, gear inches are a convenient way to describe the gearing you are in when in different combinations of the front chainring and rear cog (taking into account wheel and tire size and crank length [edited to add: see discussion in comments regarding this; seems that I did misunderstand.]). The lower the number, the easier the gearing. For example: The lowest gearing possible on my Rivendell is 26 gear inches. The lowest gearing possible on the Royal H. Randonneur is 27.6 gear inches. The lowest gearing possible on the loaner Seven is 33 gear inches. 

So, on paper, it appears that the Rivendell is geared easier than the Randonneur, and much easier than the Seven. But in fact the bicycles feel similarly easy to ride in their lowest gearing. Cycling up the same hills, I've determined that 33 gear inches on the Seven feels about the same as 26 gear inches on the Rivendell and 31.6 gear inches on Randonneur. It seems that weight, geometry, positioning, tubing, and a number of other factors play into it and that gear inch calculations are bike-specific. It is not clear to me why some seem to suggest that gear inches are independent figures that one can use to determine the appropriate gearing on any bike. 

---

Edited to add: My "what am I missing or misunderstanding here?" question has been answered in the comments; please read through them for an interesting discussion. I was mistaken in believing that crank length is factored into gear inch calculations; it is only factored into gain ratio calculations (an alternative way to measure gearing). When comparing gain ratios between the three bikes, the equivalently-experienced gearing on the Seven and on the Randonneur are in fact the same, whereas the equivalently-experienced gearing on the Rivendell is a bit lower. So... while other elusive factors remain, it appears that crank length is a huge one and that calculating gain ratios instead of gear inches allows you to factor it into the equation. Please continue to contribute to the discussion if you feel there is more to it, or that I phrased something incorrectly. I would like all of this to remain here for others' benefit.