Krypsyn: I am not sure how Bioware arrived at the 161,000 XP limit for TotSC. It seems pretty arbitrary, unless they just REALLY wanted to let thieves get to level 10 :P (160,000 XP req.). It isn't even double what the base game cap was, since that cap was 89,000 XP, iirc.
Regardless, as Shadowsetzer wrote, those spells ARE in the game, however they can only be used from scrolls. Just because a spell can't be cast from your spell-list doesn't mean it shouldn't be in the manual. There are tons of level 5 spells, cleric and mage both, scattered around the game-world. Lastly, maybe when they planned the manual, they hadn't firmly decided on the balance for the game yet (highly probable), so they wanted to leave themselves some wiggle room for setting the XP cap.
All in all, I think too much information is a manual is highly preferable to too little. ;)
EDIT:
Totally forgot about druids when i posted this. Druids also use many cleric spells, and they can make it to level 10 in TotSC (125,000 XP req.). However, they couldn't get 5th level spells in the vanilla Baldur's Gate, since that would require 90,000 XP (for level 9). This is quite possibly why the XP cap for the non-expansion game experience cap was set at 89,000 XP: so they could keep druids and clerics more balanced. Honestly, though, getting level 5 clerical spells would be about the only reason I would play a plain druid (one without a kit or multi-class) in the vanilla BG...
cheers.
i thought only mages could cast from scrolls, which begs the questions as to why priests get 5th level spells...........?
separate question, if one dual classes as a fighter-druid, can the druid use swords and heavy armour without affecting his druidy abilities?
seems like a cheap way to get 5th level spell-casting and the extra half attack at level 7 fighter!