It is noteworthy that the Zohar writes exactly the opposite. An oath, he says, can only take effect on a davar she’yeish bo mamash, something that has substance, whereas a vow can take effect even on a matter that lacks substance.
The Shoel U’meishiv in his haskamah to the sefer Beis Yisroel cites from the Neizer Yisroel that it is a printer’s mistake and the correct version of the Zohar is the way the Gemora states.
Reb Reuven Margoliyos disagrees and cites a Ramban in Shavuos who hints to the version that we have in the Zohar. The Ramban writes that according to Sod, vows do not take effect on matters of substance, whereas an oath will be effective on matters of substance.
In the sefer Mei Hashiloach, he explains the Zohar in a manner that is identical to our Gemora. We find in the Zohar that a davar she’yeish bo mamash frequently means something that has the ability to reproduce. The reason that an oath can take effect even on intangible matters is because an oath is an issur gavra, one is prohibiting himself from the object. The oath, therefore, is taking effect upon the person. The meaning of the Zohar is that an oath takes effect on the person, for he is a davar she’yeish bo mamash, i.e. man has the ability to reproduce; objects do not! An oath takes effect upon the person and not on the object. A vow, on the other hand, takes effect even on a davar she’ein bo mamash, something that does not have the ability to reproduce, i.e. objects. For by a vow, one is prohibiting the object upon himself (issur cheftza), and therefore, the vow takes effect upon the object, not upon the person.