Why 40th level?

[Mustrum_Ridcully]

The level cap will be raised in the expansion.

You know the rumors about Upper_Krust working on his 4E version of the Immortal Handbook?

They ain't rumors.

The rumor I am making up right now that he will be selling it to WotC!

 

[CapnZapp]

I would hardly be surprised if Wizards in a few years time succumb to the temptation to sell more crap to its customers, by disregarding everything the current designers fought for, and writing a splatbook for adventuring past level 30...

 

[-Avalon-]

Some groups do not fit the mold. I have heard podcasts and read stories of groups who have problems handling evenly matched encounters, as well as groups who take n+4 encounters and eat them for breakfast, not even dropping a daily to finish them off...

My guess is, they gave the DM's some room to finesse things for their players. I agree n+10 sounds a bit extreme, but with a very efficient group and a loose DM (more treasure, gold, etc)... could be feasible to have groups who could handle that sort of thing...

 

[Danceofmasks]

The PvP/Penny Arcade podcasts don't count ...
They were:
Poorly built pregen characters.
Players are all new to 4e, as well as not having any rulebook access.
Were not given appropriate gear when they were "leveled up" in the later podcasts.
They were a party of 3 with no striker (small parties end up in encounters vs. fewer enemies, so striker > controller).

That combination of factors got them pwned ... their gameplay wasn't bad, and if just one of that bad stuff was, well, less bad, they would have been ok.

 

[Jhaelen]

Well, if you're using the encounter templates from the DMG you already require level 37 monsters (a Hard wolfpack encounter using three skirmishers for a level 30 party).

If your party has more than five members you may want to use monsters with an even higher level. Or you may want to create an overpowering encounter that isn't meant to be beatable, e.g. the party tries to slay the central deity of your pantheon.

IIRC, one of the developers mentioned that a deity like Moradin would probably be about level 40 and shouldn't be beatable without the aid of appropriate artifacts, unique rituals or other plot devices.