Re: the difference is much more pronounced ...
I really don't understand your point- of course the BtN list isn't going to reflect the SSA list exactly because we're a small sample size that actually *isn't* the same as the general population even though we are apart of the general public. It is what is known as a "sampling bias". That is why you try and get a representative sample in any kind of research if you want to generalize your findings to the "general public". Rachel Shaina isn't trying to do that- she does this for her own interest and for ours.
We have a sampling bias because even though anyone can post on these boards, most don't. The people who post here are mostly female, are generally more highly educated or at least read more than the general population, have an interest in names (therefore are less likely to pick a name they just hear regularly like Isabella), and actively spend time weighing the pros and cons of names. Of course it won't reflect the SSA charts, just like if you took a sample of children of college professors or a sample of children born in a small Southern town that is mostly African-American- it won't be anything close to the SSA charts but still might be interesting just because it does reflect that sample. It just won't be generalizable to the population at large.