Windjammer
Adventurer
Well, let's look in the DMG 3.5, p.50,
under the Heading Difficulty and the subheading Challenging:
That is a guideline for encounter design - obviously, it also is a guideline for CRs, since a single monster has an Encounter Level equal to its CR.Most encounters seriously threaten at least one member of the group in some way. These are challenging encounters, about equal in Encounter Level to the party level. The average adventuring group should be able to handle four such challenging encounters before they run low on spells, hit points, and other resources. If an encounter doesn't cost the PCs some significant portion of their resources, it's not challenging.
I'd like to alert you to the context of the quote you provided, and direct you to this site: http://www.thealexandrian.net/creations/misc/encounter-design.html
A: Most level appropriate encounters deplete 1/4 of the party resources.
B: A level appropriate adventuring day consists of 4 of those level appropriate encounters.
B does not follow from A.
A is not a definitive statement of what a level appropriate encounter consists in. Because, unlike a bazillion of forum posts, that statement doesn't actually talk in terms of absolutes (exceptionless generalities).
And while we are at your quote from the 3.5 DMG,
C: "Most encounters seriously threaten at least one member of the group in some way."
doesn't exactly entail
D: "No encounter should seriously threaten that member in the party whose player can only think of hitting things with metal swords."
either.