There should be no confusion about e- resources and web resources both are synonymously used. the concept of e- resources is broader than web resources. Web resources contain only online ( internet based) resources on the other hand e- resources includes the CD ROM databases, DVD, Optical storage etc., ( including web resources) which can be read with the help of machine. ( Either computer or microfilm reader) the internet connection is not necessary to read these resources.
i will agree with saini further to add in case of cd/dvd resources once you procure you can use number of years what ever contents it had,but no updates.Usualy where updates are not many u can procure alternate years or so depending on your budget. Incase of intrnet based connectivity renewal may become must.