>> Of course, some ideas are just bad, but I'm convinced loads of start-ups that failed could have been made to work given sufficient time.
Are some businesses under capitalised? Sure. Could "loads" be saved with more capital? Well yes, for some definition of "loads".
But annedotally I'd suggest that "most" are just bad ideas. Or perhaps more accurately "incomplete ideas".
To be a success business you need;
A) a product
B) a market for the product (ie people who would actually dip in their pockets)
C) that you can reach via marketing
D) that can afford the product.
The vast majority of business ideas have A, a few do B but its very rare that they consider C or D.
As techies we're all about A - build it and they will come. But a successful business needs all 4 - miss one out and you fail.