I've been having the same issues here in Greece during the past 2-3 days. Both my iPhone 5s and iPad Air are showing a bunch of updates available for me to download (on the App Store app), but for some very strange reason my MacBook Pro w/ Retina Display does not find any updates available to download (even though I have over 450 apps on my Mac, which usually means I have a bunch of updates to download daily). I've also re-installed iTunes on my MacBook Pro, per the Apple advisor's advise which I spoke earlier today, but that did not fix the issue. I'm able to download the updates on the iOS devices directly and on the MacBook Pro by visiting the iTunes Store and look for each app separately, but I'm unable to download the updates by clicking on the "Check for Updates" button on iTunes (v. 11.1.3 for mac).
Additionally, during the past 2-3 days, when I try to sync my iOS devices with my MacBook Pro, the mac will not install any apps that I've updated on my mac directly (by visiting the iTunes Store on the mac and doing a "manual" update). I'm able to sync other content on the iOS devices from my mac, but not any updated apps.
I got a case number from the Apple advisor I spoke to earlier and waiting supposedly to hear back from Apple engineering. Let's see...