The phrase is widely attributed to Thomas Bertram Lance, the Director of the Office of Management and Budget during Jimmy Carter's Presidency. Bert Lance believes he can save Uncle Sam billions if he can get the government to adopt the motto,"If it ain't broken, don't fix it!" He explains,"That's the trouble with government: Fixing things that aren't broken and not fixing things that are broken."
It's certainly true that there are sometimes things that don't necessitate replacement, but we often put off replacing or fixing things due to our own complacency, being penny wise and pound foolish. Or by having a cavalier attitude about threats to business continuity by being under the naive assumption that horrible things will never happen to us, they happen to other people instead.
The last time the industry hopped on the clue-train was the Year 2000 problem. Countless IT professionals worked full time for several years in the remediation of software and systems in anticipation of that event. Had the date field correction not been made, transactions on many systems on the morning of January 1, 2000 would have reverted to January 1, 1900. The results would have been catastrophic for infrastructure, banking, and any system that has date dependent transactions. The world-wide cost of the remediation of that bug has been estimated at over $300 billion. IT support during the evening of Dec 31, 1999 were told to stay at work and forgo the usual New Years Eve festivities. On the morning of Jan 1, 2000, nothing happened. Very few systems around the world were affected. The reason why nothing happened is not because the Y2K bug was overblown, but it was because IT was proactive and it did its job.
Just like Y2K, ignoring Windows XP's end of life is another catastrophe waiting to happen. There's no magic date where systems are going to just blow up. Instead, after security patches and updates for Windows XP ceases, it will be open season for hackers attacks against the OS that cannot be defended against.