Make blends between the first and last steps in each row and choose 8 in-between steps. That way you'll get 10 squares.
You can expand the blends afterwards if you wish.
your technique is flawed for the result I'm after,
I want to make a hundred (100) different squares not ten.
I want to make ten columns and ten rows... Starting at 100% Yellow and 100% Magenta in the upper left to 90% Yellow to 90% Magenta by increments of 1% in the lower right.
This is easy in all Illustrator before CS 5.
No blend trick and multiply this mumbo jumbo.
No. I meant of course one blend for each column.
Although I think the example you give has far too many steps and is visually confusing.
Wouldn't 5% between steps be much better?
Blending would be so much easier than creating the rectangles and coloring afterwards.
1. create 4 rectangles for all edges
2. make with two blends: top row and bottom row to create the steps
3. Expands both blends
4. then select top and bottom in each column and blend the columns
all in all this will take you about 1 minute