I'm going to make a clear cut statement which is of my own personal opinion, but seems to be equally and adequately reflected in statistics widely available and accessible.
Google is the most used search engine in the world. Facebook is the largest social network the world has ever seen. Windows still runs on the vast majority of computers worldwide. The iPhone is second to none to any other single mobile phone or handheld device in modern times. And sliced bread has yet to be improved after its initial conception proved well enough.
These may not be the very best of what their each respective category can achieve, but they are certainly the most popular. One could ask simply "why?" as someone who studies a social science, I usually throw that around the office at least twice a day. But a more interesting question is "when?" - a reference to a time where they could no longer be the superpower of their each technological area.
It's not to say that it would be impossible for a product or device to replace the aforementioned, but let's face it - it's unlikely. Mac's will never replace Windows, and Google will always be ahead of Bing. The BlackBerry can try, but the iPhone will get stronger each time it's revamped, and sliced bread is just... well it's just wonderful, isn't it?
In my view, because these are the top of their game and are raking in more money per annum than most Western governments can lose in a financial year, it would be almost impossible for a rival product to replace them.
A new way of using mobiles and operating systems will eventually render Windows 'useless', or rather the software companies will simply replace it with an alternative like 'Midori'. Maybe Google will switch focus from search to something else, though it's unlikely as it's heart is in search and has created a brand of which nobody else could compete with. Perhaps Facebook will collapse under intense pressure from future governments over serious data breaches or privacy concerns?
We can only guess. These products do have an end game, but the chances of them being overtaken by a rival just seem so very unlikely.
From here, it's difficult to even contemplate the future of the technology industry as we see it today. So many variables and with so much time and economic uncertainty, along with a blend of public perception and marketing techniques, it is near impossible to gauge where it will take us.
Though I think many of a subjective and unbiased perspective will agree that, almost whether we like it or not, these 'companies on top' are probably not going to change any time soon. There is a reason why sliced bread didn't develop any further; there was no need. If something isn't broken, why change it?