I agree with the first sentence, uptime is a very nice thing that users will notice and appreciate over time.
However, I strongly disagree with the second sentence. Investing is uptime is not always worth it. Taken to its logical extreme, imagine 2 potential websites. One of them is incredibly useful but only up 80% of the time. The other one is a blank HTML page, but it the most reliable website in history with 0 seconds of downtime in the past 10 years. If I surveyed users of both websites, I think it would be almost unanimous that people preferred the useful website that was up sometimes.
Startups have limited time and resources, and in practice getting 99% uptime is relatively easy, whereas 99.9% uptime is relatively hard. That is a difference of ~7 hours of uptime per month. Yes, it sucks when your website is down, but it also sucks when there are features you can't develop because you don't have the time or your technical infrastructure doesn't allow in order to chase ultra high reliability. Obviously this depends on your industry, IE if you are a payment processor you better have super high uptime or you aren't going to have any customers, but realistically most companies will likely not lose that many customers if they are up >99% of the time.
There's also risks inherent in a more complicated system.
You can engineer a more complicated system with the goal of avoiding downtime, but this added complexity may end up with unexpected corner-cases and cause a net decrease in uptime, at least in the short term.
It's often better to concentrate on improving mean time to repair (MTTR).
However, I strongly disagree with the second sentence. Investing is uptime is not always worth it. Taken to its logical extreme, imagine 2 potential websites. One of them is incredibly useful but only up 80% of the time. The other one is a blank HTML page, but it the most reliable website in history with 0 seconds of downtime in the past 10 years. If I surveyed users of both websites, I think it would be almost unanimous that people preferred the useful website that was up sometimes.
Startups have limited time and resources, and in practice getting 99% uptime is relatively easy, whereas 99.9% uptime is relatively hard. That is a difference of ~7 hours of uptime per month. Yes, it sucks when your website is down, but it also sucks when there are features you can't develop because you don't have the time or your technical infrastructure doesn't allow in order to chase ultra high reliability. Obviously this depends on your industry, IE if you are a payment processor you better have super high uptime or you aren't going to have any customers, but realistically most companies will likely not lose that many customers if they are up >99% of the time.