Please keep in mind that both DV (standard definition on mini-dv tape) and HDV 1080i (High definition on mini-dv tape) use the exact amount of harddrive space. So its not really a crazy amount considering, but for more detailed breakdown:
DV and HDV 1080i 25 Mb/s
25 Mbits / second
25.600 bits / second
3200 bytes / second
3,125 Mb / second
187,5 Mb / minute
11,250 Gb / hour
if you get 13 Gb/hour it is probably because of the fact
1) Tapes are about 63 minutes
2) This is the actual size of files, size of files on a HDD might be different (1000 - 1024 difference: E.g. 1,5 Gb is not the same as 1 Gb and 500 Mb)
HDV 720p (19,7 Mbits/second with the audio included)
19,7 Mbits / second
20.173 bits / second
2522 bytes / second
2,46 Mb / second
147,75 Mb / minute
8,865 Gb / hour
So, taking everything in account, 1 hour of DV or 1080i HDV is about 11 Gb and 1 hour of 720p HDV is about 9 Gb.
Oh and your MBP will handle HDV like a champ.