I see it done less with customary, because they often spell the units out, i.e. 36 inches, not 36 in., therefore making the space more necessary.
As for the email copy, it seems to me that it was copied out of a British press release. Note the spelling of color as colour. J&R is a NYC-based retailer. Clicking the link through to their website shows the following copy:
"measuring 9.9mm thin (less than 1/2 inch) and it weighs at about 26 pounds" D'oh! Paul Trusten wrote:
...except for leaving a space between the unit value and the unit symbol (e.g., 15 kg). It just occurred to me that, perhaps people leave out the space because they think they are performing an algebraic multiplication. No matter what the reason, I find it almost rare that people get this right. Somehow, I don't think they do it as often with inch-pound units. Or, do they?
