And then, there's the fact that there is no universal HB scale (..or is there?). A HB7 for you, might be a HB9 for someone else, and vice versa.
Plus, I bet that the scale shifts depending on the quality of women you have had the chance of ; Coming from a place abundant with "Super-hot-babes"(tm), I remember being called chauvinist and "ridiculous in my standards" while in United Kingdom, since I found huge majority of girls there sub-par (i.e., 80% of women were <HB7 in my eyes).
What I've noticed, though, is that there seems to be a general "ratio" in our heads of rating HB's by abundance.
Allow me to explain:
Say you live in A, and the percentage of HB7/HB8/HB9/HB9.99's one meets is 15/10/5/1%. So, one out of seven girls is a HB7, one out of 10 is a HB8 and so on (rates may vary)
If you move to a new place (B) and suddenly find yourself meeting HB9's 10% of the time (1 out of 10, instead of 1 out of 20), subconsciously you relegate them to HB8's over time, since the general numbers show there can't be that many HB9's out there, and whole quality scale shifts, introducing hotter girls than you ever met at the very top of the scale.
The quality of women, therefore, in B is somewhat higher than in A. However, if you spent your whole time in either A or B, there is no way to find out how that quality is different in your place compared to others.
Now, I don't think it works exactly the same if you moved from B to A. Sure, scale may shift somewhat, but since you have seen the quality of HB9's at B, the same women regarded as HB9's in A are now only HB8's in your eyes. Just like once I've got a 40" TV, I couldn't get back to using a 21" TV - once you get a taste of better, it stays.
And now, with advent of internet/tv media, it is easy to get to see the top of the scale, and reserve the HB8.5+ spots for the very gorgeous women that are very hard to find; Look at some random scary movie or something - the girls there are often handpicked babes, all HB8.5-HB9.5's. However, since that is all the girls you see when watching the movie, you subconsciously spread them out to "fit the scale", so the HB8.5 becomes "Meh, she's a seven, I guess" and so on;
So, are you sure you are not rating girls you are getting with too low? Would you mind posting examples of what you would call a HB7/7.5, since I'm rather curious (I don't mean *your* HB7/7.5's, I mean some random girls of the net that fit into the rating for you)?