Maurici,
For some people, this may be the case. It really depends on what comes out of your tap. Bill and I are both in the San Francisco Bay Area, and we are both supplied by East Bay Municipal Utilities District (please correct me if I'm wrong, Bill), but the water treatment plants specific to our locations give us very different water. In my area, the water is very soft - dKH and dGH are often times 1 or less. Bill has explained to me that his tap water registers at 13 or 14 dH. Plants in my tank are probably more likely to suffer from deficiencies if I did not add nutrients. In some parts of the country, people have some ungodly levels of nitrates right out of their tap - way higher than our target level of ~10 ppm; here, it's below what our test kits can detect. It really depends on what sort of treatment our water goes through.
Bill - this is from a different post, but I'm wondering what's happening to your L. sp. 'Cuba.' Are the leaves still growing out looking like sunset hygro or have they resumed "normal" growth? I noticed the ones still at the shop did the same thing as yours, but eventually started to put out the normal-looking leaves. I'm wondering if maybe this species has an "adjustment period" during which it does weird stuff like that...? Just so you know, they don't add fertilizer to their tanks so the weird growth thing may not have had anything to do with a deficiency (since it did go back to normal growth without fertilizer). I know their plants sometimes show very poor color toward the end of the first week and into the second week after receiving the shipment - this is likely the result of lacking nutrients. They merely survive and grow due to good lighting and CO2 injection.
-Naomi