I hadn't noticed that... are there 10th Level spells in 4e? In the previous editions, if I'm remembering correctly, spells topped out at 9th Level (and in 2e and earlier, at 7th Level for Clerics, IIRC). I never understood why.
That reminds me - I wish they would come up with a new term for caster level and spell level... it could be confusing at times trying to differentiate the two for new players.