My bitcoin-qt client connection status and uptime at http://blockchain.info/connected-nodes does not show reliably - why? I've been running a Bitcoin-qt client (v0.7.2 beta) on my Mac for over 24 hours, with blockchain fully sync'ed.

I checked http://blockchain.info/connected-nodes at various times for my IP address. In the first few hours my IP appeared in the list. Then it disappeared for maybe 10 or 15 hours. Currently, it's back in the list, but showing a connection time of only 62 minutes, despite my network connection and IP address being completely stable, and a steady stream of inbound &amp; outbound network traffic to/from the Bitcoin-qt client during the entire >28 hour period since I started it up.

Why would my IP show up at http://blockchain.info/connected-nodes for a certain time, then disappear from the list, then re-appear?

(It also appears that, as of this writing (2013-02-19  18:02:30 UTC,) no client on the list has a connection time of more than about 340-360 minutes. I'd expect it to be in the thousands to tens of thousands of minutes for at least some clients.)
The list on http://blockchain.info/connected-nodes is just a list of nodes currently connected to that specific business' bitcoind server. It has no connection to the list of all Bitcoin nodes connected to other nodes. This hypothetical list doesn't exist anywhere, for obvious reasons, and would be 10 to 20 times longer than blockchain.info's list.

Blockchain.info's server is not authoratative in any way and has no formal connection to the "official" Bitcoin client (bitcoin-qt), the Bitcoin project, or Bitcoin.org.

As for the 360 minutes thing, Blockchain.info's bitcoind server probably prunes clients connected for 6 hours for whatever reasons that business has decided to do that. Or perhaps their bitcoind server lost its internet connection momentarily around 6 hours before you checked their connected nodes list.