Really agree here, the seedsman wants his customers to have a good experience, then they may come back, so he gives the best information he can for growing.
Of course, as you say later, local conditions can vary, and the set parameters may be 'ideal', but if you want an early or late crop, or even to extend your cropping season, you can usually stretch them. Your planting time or place may not be 'ideal', but it will often give you a good crop all the same. Seeds are very cheap on the whole, it will really only cost you in space to experiment a bit.
Having said that some seeds and plants are expensive. Unlike most commodities this is not because they are 'better', but because they are harder for the seedsman to grow successfully, and therefore harder for you too. It often pays to go for the cheap option, look at marigolds!
