From the documentation I see it\'s possible to create a laravel project via laravel installer:
$laravel new blog
or via composer:
Just tried both ways and in both ways I got generated .env file:

Composer should automatically create .env file. In the post-create-project-cmd section of the composer.json you can find:
"post-create-project-cmd": [
"php -r \"copy('.env.example', '.env');\"",
"php artisan key:generate"
]
Both ways use the same composer.json file, so there shoudn't be any difference.
I suggest you to update laravel/installer to the last version: 1.2 and try again:
composer global require "laravel/installer=~1.2"
You can always generate .env file manually by running:
cp .env.example .env
php artisan key:generate