I have a similar situation
I updated my shop channel so i could use it to see what was new
When i updated the internet channel from the shop channel it said i had 34 blocks free
I couldnt beleive by system memory fell so low
The internet channel said it was going to take 0 blocks for the update so i let it go through
After the update i had 67 free blocks, it went up for some reason
So I updated the nintendo channel, it also said the update would take 0 blocks
After that update i have 86 free blocks
Everything I can dl from the shop channel says it will take 0 blocks
When I go to the data management the wii says it has 198 free blocks
I cant figure out why