If you happen to look on exactly the right page (and only this page?) and then see the tiny "see exceptions" link and read it carefully, then you'll get it. It's technically findable. FTers have learned about it (see the FAQ) and know where to find it. But here's why I argue that it is hidden...

1) I don't see any warning while booking. There should be one.

2) Their page about earning points (http://www.accorhotels.com/gb/leclub...nts-stay.shtml) would be a fine place to note the exclusion. Instead it says "With Le Club Accorhotels, you earn points on all stays at one of our 2,800 hotels by booking directly via:" This is the opposite of warning about exceptions. It should say "(see list of exceptions here)".

3) They have a warning on the same page about not earning points:
"PLEASE NOTE, NOT ALL BOOKINGS EARN POINTS!
Bookings made via online travel agencies (i.e. Expedia, Booking, etc.) do not enable you to earn points on your stays." This would have been an excellent place to add "Nor do stays at IBIS budget,..."

4) The IBIS.com page covers the "IBIS family": IBIS, IBIS Styles, and IBIS Budget. Their page on earning points makes no mention that 1/3 of their sub-brands don't earn points. http://www.ibis.com/gb/leclub/index.shtml The closest they come at any point is where it says "Every time you stay at ibis and ibis Styles, Le Club Accorhotels rewards your loyalty." I suppose an astute reader would notice the omission of IBIS budget and wonder whether that's included under "IBIS" or whether they are excluded. But shouldn't they just mention the exclusion explicitly? It's real easy, unless you want to hide it.

5) They have a web page devoted to "Discovering IBIS budget". Do you think it's mentioned anywhere there? http://www.ibis.com/gb/europe/discov...el/index.shtml

P.S. My hotel wasn't $15, it was $56+, which makes me feel even more foolish.