kcire, your observations are very pertinent and your question valid.

The World Wide Web Consortium (W3C) and others, have, over the years, developed various languages/technologies with the aim of creating compatibility amongst the dozens, if not hundreds, of browsers in use. Without the rules the internet would become too chaotic and an inevitable exclusivity would develop. How many times have you seen 'Best viewed in IE5+ at 800x600'? What about blind people with text browsers or Netscape users?

As with national languages, if you want to be interpreted correctly by most it's a good idea to speak or write clearly. Unlike spoken or written languages which are full of variations and subtle nuances, the languages of the web are interpreted by unintelligent machines! Whilst the browser writers have developed ways around errors like missing end tags or quotation marks, errors at best slow down load time or at worst turn pages into dog's dinners! The browsers appear finally to have agreed a level of compliance, for everyone's benefit. As web designers we should celebrate this because it frees up our time to focus on the most important issue which is the content, layout and functionability of the sites we build.

You are right about http://www.sitereportcard.com/ and the warnings it generates. Also check http://www.google.com and my favourite sites like http://www.bbc.co.uk/ and http://www.guardian.co.uk/. Even the best designers get it wrong sometimes but that's no reason to not bother ourselves. Either they'll get it right or the <DOCTYPE> will be adapted to accommodate worthwhile developments.

Those working on the biggest sites don't need to worry too much about search engine placement but poorly put together sites do less well in the search engines for good reason. Chances are the content is suspect too. Would you buy a computer from a website that pops up error messages? Would you credit a scientific theory if it was peppered with spelling errors? Probably not, so Google et al will probably bury them deep. OK, so you don't have to get 'perfect' on all of the tests, sometimes it's impossible but you can still have a good go at it.

I haven't been visiting this forum for very long but I noticed a lot of sites submitted for review contained sloppy errors and typos. So I posted some useful links that I use myself (these days!) because I reckoned most people submitting sites actually wanted constructive observations about their layout and navigation, speed to load and usability. The validation, accessibility, spell-checking and search engine readiness tests are objective and are best dealt with by unintelligent machines!

I hope this answers your question.