FWIW, Google Search still uses <b> tags for byte-saving reasons. Search terms are all bolded, and the page would become significantly heavier if those were <strong> or <span class=...> tags instead of <b>.
(There's some crazyness where they actually become <em> tags in China and are styled differently, because Chinese typographical conventions avoid bolding characters and instead turn them red for emphasis. I tried to simplify this once and do everything via CSS, but it turns out to be quite complicated because you also have to handle the case of interface text that's not in Chinese and supposed to be bolded, and exceptions for single-character words, and mixed English/Chinese text, and other languages like Arabic that run RTL, and mixed Arabic/English text, and presumably mixed Arabic/Chinese text though I've never seen such a page. It turns out CSS is fairly limited when you get into the complexities of human typographical conventions across the globe.)
As I noted below, <b> and <i> are meant to be typographically-significant elements, so it's not just byte-saving. Google is using <b> and <i> correctly in that case (even if that's just a happy accident).
(There's some crazyness where they actually become <em> tags in China and are styled differently, because Chinese typographical conventions avoid bolding characters and instead turn them red for emphasis. I tried to simplify this once and do everything via CSS, but it turns out to be quite complicated because you also have to handle the case of interface text that's not in Chinese and supposed to be bolded, and exceptions for single-character words, and mixed English/Chinese text, and other languages like Arabic that run RTL, and mixed Arabic/English text, and presumably mixed Arabic/Chinese text though I've never seen such a page. It turns out CSS is fairly limited when you get into the complexities of human typographical conventions across the globe.)