Being a thousands of followers in telegram on a ICO project is better for them to attract more investors and contributors. But telegram is just one of the platforms that support the ICO. Like social media, blog and articles, bounties and more.
Yes, I agree here, diversifiying a marketing is a very good measure to make their own project more famous and attract new investors. For me it's most important all the channels are updated often enough so everyone can follow the progress. And an official Telegram update group, where you haven't to read all the spam questions.