I think the term startup is in fact somewhat misleading, because in many cases venture capitalists that want to invest in these organisations want them to have

I think the term startup is in fact somewhat misleading, because in many cases venture capitalists that want to invest in these organisations want them to have a full business plan and evidence of customers / market leverage. Obviously it makes sense for them to ask for these things, but to me it seems odd to call an organisation with a long term plan and often a number of employees a 'startup'. Organisations that are truly starting up are in much earlier stages of development, trying to decide if there is a market for a particular product and trying to fit this market and generate interest. But the definition you give of a startup seems to be the current interpretation that many people would have.