Sim, é de 32 bits por padrão, por motivos de compatibilidade do plug-in. Por comentário da Microsoft:
On 64-bit Windows 8, the browser frame process (both “modern UI” and Desktop) runs 64-bit. However, for compatibility with plug-ins, IE 10 on the desktop runs 32-bit tabs by default. If the user turns on “Enhanced Protected Mode” in Internet Options, Advanced; they will have 64-bit tabs by default for IE 10 on the Desktop.