There is probably a lot more room for improvement. Anyone wanting the sample before buying may be quickly turned off. It's a 60MB zip file because the audio is bundled in. This easily deters anyone on their iPhone/iPad.
Not just iPhone/iPad - my broadband's not so very fast when the kids are watching something on NetFlix, and it's dismaying to have that large a file to wait for.
(I bought the book anyway - you should probably give Daniel a kickback, actually.)