I think that's actually pretty cool since there aren't a whole ton of places for park-goers to shelter.
I don't think DLR has ever kept closed all day for weather, but they do often close early when it's raining, especially on weekdays. On one hand it makes sense, with lighter crowds and unfavorable conditions, but on the other hand it really stinks for the guests who paid to be in the park that day. It just sort of reinforces the idea that southern Californians are total weather wimps and can't handle anything that's marginally inconvenient. Other that hurricanes (which can keep things closed for a couple days), I'm not aware of WDW's parks ever closing early for weather; certainly not for an ordinary rainstorm
