The only one whose exclusion bothers me is the calculator app. I think Apple would've been able to make some awesome improvements to it on the iPad. Every computer needs a good calculator app. As far as Clock, Weather and Stocks go, Apple probably believes that they won't be as useful on a non-pocketable device such as iPad. Stocks is pretty much a business oriented app so I'm not entirely sure how useful a native client would be on the iPad when you can just visit any website. I expect Apple feels the same way about Weather, since the iPad is less likely to be carried outside of home. Clock (alarm, timer, stopwatch, etc..) is also more useful on a handheld device than on an iPad.
I've been able to find some decent replacements for above apps, however:
Stocks: couldn't care less, though there are probably good alternatives on the app store
Calculator: PCalc Lite (free);
HiCalc Calculator (free);
HiCalc Calculator Pro (11 in 1) ($0.99) - amazing app for the price
Weather: Weather+ (
$0.99); (
free); Fahrenheit (
$0.99) (
free); Weather Live (
$0.99) (
free);
Thermo (free)
Clock: Classic Clock (
free) (
Pro $0.99);
Best Timer ($0.99)
EDIT:
Voice Memos: Voice recorder for iPad ($0.99);
MegaRecorder HD+ ($0.99); also
GarageBand ($4.99) has recording functionality.