My impression is that those trade/tech "expos" in the 19th century were really a massive acceleration force of innovation and industrialization. To the point that I could imagine that the lack of such expositions might be an explaining factor why the Roman empire never experienced an industrial revolution. Nowadays they're less important because they've been replaced by conferences (which are the same idea dialed up to 11, I'd argue, and no less important in driving innovation). Maybe I'm going completely off here, but would be interesting to read an analysis.