Book review sections in newspapers have certainly died. But, interestingly, some magazines are expanding theirs. I believe the Atlantic is one.
My reply to anyone who says: "Book reviews are outdated" would be: Come back and tell me what you think after you get your first review in, say, the Washington Post. Reviews in the pubs that have book sections can still have an enormous impact, less in terms of catapulting you on to the bestseller lists (which tends not to happen now) but setting you up for grants, awards, TV, appearances and much more.
Whether or not they still matter, in other words, depends on what matters to you. Speaking just for myself: I'd much rather have a great review in the NYTBR than countless five-star reviews on Amazon. Nobody will remember those five-star reviews in 10 years, but a great review in a major pub lasts forever: Your children and grandchildren will still savor it.