Here is why that is an over-simplicification, and to most intents and purposes, completely wrong.
This means that menus created in those ways are indexable in a way that is virually identical to HTML only or HTML/CSS menus. There only differences perhaps being the subtle nuances of importance implied by the particular HTML mark-up used.
There are a few things to avoid though:
Secondly, don’t “hide” HTML in an unsafe manner. Search engines expect to find hidden div layers for navigation (several people believe hiding HTML will incur a search egnines wrath as an extension of the issue I’m about to highlight here). However, search engines are also on the lookout for sites “hiding” text content from users for no good reason. If your hidden HTML contains text significantly more than links, it is likely to look like a cheap attempt to cloak. Even links set up in a non-menu way might trigger suspicion. Avoid hiding div layers by poisitoning them with negative left margins greater than their width, and so on. These are red flags to Matt Cutt’s spam police, even though they could be forgivable for a menu. Avoid anything that puts you on the radar of the spam police!
Finally, don’t use use CSS to hide any other text on your page without good reason – for example as storage for text used in a marquee display – as this is almost certain to trigger spam filters and bring you to the attention of Matt Cutts’ team. He’s a nice guy, but he’s a trained spam killer!