Yes, you are right. I hv missed that point in the article.

Most of the search engine (including google, yahoo, altavista etc) will crawl your ALT text which can help improving the ranking of your website but please note that it will not make big impact on the ranking.

ALT tags also make your site more accessible to visually impaired people using text readers. That's because text readers can't read images, but can detect text in ALT tags.