BJCP state IBU of 40 to 60 (English) and 40 to 70 (American).
I think a factor is that if you are a regular IPA brewer and a hop head your palate definitely changes. I'm convinced that a lot of the posts you read about "Whatever happened to JS Amber Ale, it's not like I remembered", and "Fat Yak has been emasculated".
I'll reveal that I was tee total for six years following a bit of a breakdown in the early 1990s and got back into it in 2000. Even though I wasn't brewing I still remember the first few months of beers - the likes of XXXX and Melbourne Bitter were delicious, malty and hoppy - even the odd VB had some charm. Now of course they taste like mouse piss and I'd put that down to my changed palate.
I'm not a hop head, I prefer rich malty beers with hop accents, which is why I took up AG because it's the only way to produce really authentic UK Real Ales that usually come in sub 30 IBU. When I'm out and about I find that White Rabbit Dark on tap and JS Amber are as hoppy as I like, but I'm looking forward to trying the IPA out of interest.
Edit: I had a few HBs yesterday with my brew buddy round the corner. We both agreed that the reason neither of us buy "Craft Beers" at the bottlo - even though there is a big range locally - is that whenever we try one, we almost always find it a bit "meh" and samey. Here comes that NS and Amarillo again and what is
that cheesy background note many of them have? We both far prefer own brews. So we had a bit of a chat about "palate change", or more like "palate creep" I guess.