I think the reason many scripting languages lack declarations is the same reason Perl lacked them until version 5. These languages have tended to evolve, rather than being designed by a committee before the first line of code was written. Perl has evolved a form of safety, and also appears to be the only scripting language that has sensible and consistent variable scoping rules. Python hasn't got that, but it has evolved other cool stuff, like generators and comprehensions -- I often wish Perl had a simple equivalent. PHP... okay, I can't think of anything nice to say about PHP.

(And please, people, stop slandering static typing by associating it with explicit, verbose typing. Perl hackers should all be aware enough of Pugs to have heard of Haskell, and that means we should all know that it's possible for static typing to be as concise and expressive as Perl. Java isn't, but Java is mediocre by design; it's aimed at companies that want to hire a horde of replaceable cogs, instead of a handful of smart hackers working in a language that provides real expressive power but takes more skill to use.)