You’re right about the significance. I’d point out that internet connections would be vital for the outside world to follow event through channels with less risk of being biased towards the regime. Then again we’re not exactly the most prominent threat to it. 

That’s simple: it was because the Syrian government used trickery to surreptitiously capture activists’ passwords and thus access their email, contact lists, etc, making it easier to identify and arrest them.

E.g. see http://www.businessweek.com/articles/2012-11-15/the-hackers-of-damascus
“Users who tried to access Facebook in Syria were presented with a fake
security certificate that triggered a warning on most browsers. People
who ignored it and logged in would be giving up their user name and
password, and with them, their private messages and contacts.”

I’d also like to see some evidence that the Syrian government is more effective than the Egyptian or Libyan governments at using the internet as a tool of oppression. I’ve not heard that before. 
My bet is that the later shutdown has more to do with the internet’s importance; we may be experiencing the Syrian revolution via Youtube, but most Syrians aren’t. Internet penetration is less than 20%, and most access is through the dangerously public internet cafes. Download speeds are incredibly slow (wiki cites 768kbits) and broadband is non-existent – they aren’t streaming videos. Only the most privileged (and therefore most on-side, in general) have better access than that. 

(OTOH, Egyptian access, while faster, isn’t much more widely available, so I may be wrong about that being the trigger).

For that matter, pack animals laden with media quite possibly have higher bandwidth than the network infrastructure in Syria; passenger pigeons with SD cards outperformed ASDL networks in first-world countries on that one specific measure of throughput.