There are a few people who make this claim, but they seem to mostly refer to military-issue khukuris of certain vintages. Naturally a military knife is likely to be lighter weight, because it is primarily a weapon and also might have to be carried long distances on foot along with other gear. It also might lack some cosmetic features (like the HI KLVUK model). Some of the HI khukuri models would meet these war-time criteria. However, historically khukuris came in quite a variety of lengths, weights, styles, degree of embellishment, etc. It has been a cultural art-form as well as the more standardized weapons issued to Nepalese soldiers.
HI does not primarily produce replicas of military museum pieces, but usable khukuris made by traditional methods and carrrying the cultural art-form to other countries and helping to perpetuate the tradition, while providing a living for kamis who might otherwise have to seek other ways to earn a living. It is quibbling for anyone to complain that the handles are made longer to accommodate the larger hands (on the average) of westerners. It is beyond quibbling for anyone to complain about the large variety of khukuri styles made by HI kamis, especially considering that some of the styles are an expression of artistic creativity.