Width 99.9% in various panels layouts' CSS?

Minor issue. What's the reasoning for having the CSS width: 99.9% in the CSS for various full-width divs in various Panels layouts? (for example, top and bottom in two-col-stacked).

If the reason is to trigger hasLayout in pre-standards IE, I'd suggest this is a minor bug, because:

• At 501px width and above, 99.9% is at least one pixel short of 100% of the width. Depending on the design, this missing pixel can stick out like a sore thumb and require CSS patching that is sometimes inconsistent between browsers. 99.99% (or 99.999% to be seriously future-proof...) would be better
• 100% width seems to suit IE fine and trigger hasLayout fine, it's width: auto; that doesn't trigger layout (e.g. see here).

If there's no specific reason for it needing to be exactly 99.9% and no higher, why not 100% (or at least, 99.99%)?