We know learning is happening all the time with or without an L&D function. Can you imagine a company today having no L&D department? No training function? Sure, if the company is 25 people then doubtful they are having a formal department. What about 250 or maybe even 2500? Now that seems more likely - but is it necessary?
The reason a L&D or T&D department didn't exist when a company was small (25 people) was because a new worker was hired expecting to having great skill already, the company was very flexible in regards to tools, processes and policies because priority one was survival. And learning the ways of the organization happened through peer-to-peer interactions.
Today the agility often found in start-ups is not a result of trying to survive, rather survival is a result of being agile. Information and expertise is a click (or tap) away. Web 2.0 and the various tools available to help us share knowledge, collaborate and build relationships have the ability to make a 2500 employee company move like one that has only 25.
And what was the need again for L&D when a company is that small?