[R.i.m.s.k.y.]

изза чего глюки с *открыть с помощью...* возникают »

глюки не возникнут если правильно прописывать пути, вообще не столкнулся с такой проблемой.

не, эта строчка обозначает архитектуру приложения »

Specifies the 64-bit processor architecture(s) on which Setup should install in 64-bit mode. If this directive is not specified or is blank, Setup will always install in 32-bit mode.
Normally, you should not change this directive from its default value unless your application contains native 64-bit binaries.

Без этой строчки в ос64 его файлики64 не зарегятся тк Setup will always install in 32-bit mode
Ну и следствие отсутствия этой строчки - да, предлагает по-умолчанию Program Files (x86)

Там еще в помощи важное примечание: Be sure you have read the 64-bit Installation Limitations topic before setting this directive

Код:

Because Inno Setup is a 32-bit application, there are some limitations to be aware of when utilizing its 64-bit installation features:

The System32 path returned by the {sys} constant does not always map to the 64-bit System directory. When Setup/Uninstall is running in 64-bit mode, it maps to the 64-bit System directory when used in the [Dirs], [Files], [InstallDelete], [Run], [UninstallDelete], and [UninstallRun] sections because Setup temporarily disables WOW64 file system redirection when files/directories are accessed by those sections. Elsewhere, System32 and {sys} map to the 32-bit System directory, as is normal in a 32-bit process. 
In the [_Code] section, when Setup/Uninstall is running in 64-bit mode, functions that access files disable WOW64 file system redirection (unless overridden by a call to EnableFsRedirection). However, there are exceptions, listed below. These functions never disable file system redirection, meaning you cannot pass them (or get back) the name of a file located in the 64-bit System directory:

*Ini* (all of the functions that manipulate .INI files) 
BrowseForFolder 
CreateShellLink 
GetOpenFileName 
LoadDLL (see following point) 
ModifyPifFile 
SetCurrentDir 
ShellExec (use Exec instead) 
UnregisterFont 

Additionally, no VCL classes are capable of disabling file system redirection. For example, you cannot call the LoadFromFile method of TBitmap to load a bitmap file from the 64-bit System directory.

You cannot load/use 64-bit DLLs in the [_Code] section, because Windows does not allow 32-bit processes to load 64-bit DLLs (and vice versa). A 32-bit process can, however, launch 64-bit EXEs. Use the Exec function or the [Run] section to do that. 

Also, there is one limitation of the compiler:

You cannot compile a script that includes 64-bit binaries on Windows 95, 98, Me, or NT 4.0, because those versions of Windows do not support reading version info on 64-bit images.

А вот флаги 32bit и 64bit »

их НУЖНО ставить, нажми F1 и почитай
32bit
Causes the {sys} constant to map to the 32-bit System directory when used in the Source and DestDir parameters, the regserver and regtypelib flags to treat the file as 32-bit, and the sharedfile flag to update the 32-bit SharedDLLs registry key. This is the default behavior in a 32-bit mode install.

64bit
Causes the {sys} constant to map to the 64-bit System directory when used in the Source and DestDir parameters, the regserver and regtypelib flags to treat the file as 64-bit, and the sharedfile flag to update the 64-bit SharedDLLs registry key. This is the default behavior in a 64-bit mode install.