VAM does not play well when initialized from plugin/

I've tried to setup vim without a .vimrc at all, relying on .vim/plugins instead. Here's what my sample .vimrc looked like before:

" putting these into plugins did not work

fun! EnsureVamIsOnDisk(vam_install_path)
  " windows users may want to use http://mawercer.de/~marc/vam/index.php
  " to fetch VAM, VAM-known-repositories and the listed plugins
  " without having to install curl, 7-zip and git tools first
  " -> BUG [4] (git-less installation)
  if !filereadable(a:vam_install_path.'/vim-addon-manager/.git/config')
     \&& 1 == confirm("Clone VAM into ".a:vam_install_path."?","&Y\n&N")
    " I'm sorry having to add this reminder. Eventually it'll pay off.
    call confirm("Remind yourself that most plugins ship with ".
        \"documentation (README*, doc/*.txt). It is your ".
        \"first source of knowledge. If you can't find ".
        \"the info you're looking for in reasonable ".
        \"time ask maintainers to improve documentation")
    call mkdir(a:vam_install_path, 'p')
    execute '!git clone --depth=1 git://github.com/MarcWeber/vim-addon-manager '.shellescape(a:vam_install_path, 1).'/vim-addon-manager'
    " VAM runs helptags automatically when you install or update
    " plugins
    exec 'helptags '.fnameescape(a:vam_install_path.'/vim-addon-manager/doc')
  endif
endf

fun! SetupVAM()
  " Set advanced options like this:
  " let g:vim_addon_manager = {}
  " let g:vim_addon_manager['key'] = value

  " Example: drop git sources unless git is in PATH. Same plugins can
  " be installed from www.vim.org. Lookup MergeSources to get more control
  " let g:vim_addon_manager['drop_git_sources'] = !executable('git')

  " VAM install location:
  let vam_install_path = expand('$HOME') . '/.vim/vim-addons'
  call EnsureVamIsOnDisk(vam_install_path)
  exec 'set runtimepath+='.vam_install_path.'/vim-addon-manager'

  " Tell VAM which plugins to fetch & load:
  call vam#ActivateAddons([], {'auto_install' : 0})
  " sample: call vam#ActivateAddons(['pluginA','pluginB', ...], {'auto_install' : 0})

  " Addons are put into vam_install_path/plugin-name directory
  " unless those directories exist. Then they are activated.
  " Activating means adding addon dirs to rtp and do some additional
  " magic

  " How to find addon names?
  " - look up source from pool
  " - (<c-x><c-p> complete plugin names):
  " You can use name rewritings to point to sources:
  "    ..ActivateAddons(["github:foo", .. => github://foo/vim-addon-foo
  "    ..ActivateAddons(["github:user/repo", .. => github://user/repo
  " Also see section "2.2. names of addons and addon sources" in VAM's documentation
endfun
call SetupVAM()
" experimental [E1]: load plugins lazily depending on filetype, See
" NOTES
" experimental [E2]: run after gui has been started (gvim) [3]
" option1:  au VimEnter * call SetupVAM()
" option2:  au GUIEnter * call SetupVAM()
" See BUGS sections below [*]
" Vim 7.0 users see BUGS section [3]
" color scheme
call vam#ActivateAddons(['molokai'], {'auto_install' : 0})

" TextMate-style goodness
call vam#ActivateAddons(['Command-T', 'snipmate'], {'auto_install' : 0})

putting this into .vim/plugin/00-vam-init.vim did not work.

MarcWeber / vim-addon-manager

VAM does not play well when initialized from plugin/ #76