Notwithstanding these differences, the tasks are similar in nature, in that they both involve the disambiguation of textual fragments according to a reference inventory.
but while the two tasks are pretty similar, they differ in a fundamental respect: in EL the textual mention can be linked to a named entity which may or may not contain the exact mention, while in WSD there is a perfect match between the word form (better, its lemma) and a suitable word sense.