Here's the log, and some notes:

Starting state:
- Python 3.3.5 installed to P:\Python33
- Python 3.4.1 installed to P:\Python34
- py[w].exe present in C:\Windows

State after Python 3.4.1 uninstalled by python-3.4.1.msi (and manually removed P:\Python34 which still contained some debris in Lib and Scripts):
- Python 3.3.5 still installed
- Python 3.4.1 uninstalled
- py[w].exe no longer present in C:\Windows

msiexec /i python-3.4.1.msi /l*v py.log
- Installed for all users
- Destination set to P:\Python34
- Components left at default (all selected except 'Add python.exe to Path')
- Install completed successfully
State afterward:
- Python 3.3.5 still installed
- Python 3.4.1 properly installed in P:\Python34
- py[w].exe now present in C:\Windows

Picking through the log, I find that I did actually get the error the OP noted; it just doesn't seem to matter:

"""
MSI (s) (34:04) [14:27:17:664]: Executing op: ComponentRegister(ComponentId={81B1269C-979C-404A-8E3D-D297B7C38622},KeyPath=C:\Windows\py.exe,State=3,,Disk=1,SharedDllRefCount=1,BinaryType=1)
1: {DF32BB9E-3ED8-36B5-A649-E8C845C5F3A2} 2: {81B1269C-979C-404A-8E3D-D297B7C38622} 3: C:\Windows\py.exe 
MSI (s) (34:04) [14:27:17:665]: Error: cannot register 64 bit component {81B1269C-979C-404A-8E3D-D297B7C38622} on 32 bit system. KeyPath: C:\Windows\py.exe
MSI (s) (34:04) [14:27:17:665]: GetSharedDLLKey called with invalid ibtBinaryType argument!
MSI (s) (34:04) [14:27:17:665]: GetSharedDLLKey called with invalid ibtBinaryType argument!
MSI (s) (34:04) [14:27:17:666]: Executing op: ComponentRegister(ComponentId={C170DD8A-2030-4226-A15D-94E881D68233},KeyPath=C:\Windows\pyw.exe,State=3,,Disk=1,SharedDllRefCount=1,BinaryType=1)
1: {DF32BB9E-3ED8-36B5-A649-E8C845C5F3A2} 2: {C170DD8A-2030-4226-A15D-94E881D68233} 3: C:\Windows\pyw.exe 
MSI (s) (34:04) [14:27:17:667]: Error: cannot register 64 bit component {C170DD8A-2030-4226-A15D-94E881D68233} on 32 bit system. KeyPath: C:\Windows\pyw.exe
MSI (s) (34:04) [14:27:17:668]: GetSharedDLLKey called with invalid ibtBinaryType argument!
MSI (s) (34:04) [14:27:17:668]: GetSharedDLLKey called with invalid ibtBinaryType argument!

...

MSI (s) (34:04) [14:27:19:599]: Executing op: SetTargetFolder(Folder=C:\Windows\)
MSI (s) (34:04) [14:27:19:599]: Executing op: SetSourceFolder(Folder=1\)
MSI (s) (34:04) [14:27:19:599]: Executing op: FileCopy(SourceName=PY.EXE|py.exe,SourceCabKey=py.exe,DestName=py.exe,Attributes=512,FileSize=102400,PerTick=65536,,VerifyMedia=1,,,,,CheckCRC=0,Version=3.4.1150.1013,Language=2057,InstallMode=58982400,,,,,,,)
MSI (s) (34:04) [14:27:19:600]: File: C:\Windows\py.exe;	To be installed;	Won't patch;	No existing file
MSI (s) (34:04) [14:27:19:600]: Source for file 'py.exe' is compressed
InstallFiles: File: py.exe,  Directory: C:\Windows\,  Size: 102400
MSI (s) (34:04) [14:27:19:606]: Executing op: FileCopy(SourceName=PYW.EXE|pyw.exe,SourceCabKey=pyw.exe,DestName=pyw.exe,Attributes=512,FileSize=102912,PerTick=65536,,VerifyMedia=1,,,,,CheckCRC=0,Version=3.4.1150.1013,Language=2057,InstallMode=58982400,,,,,,,)
MSI (s) (34:04) [14:27:19:606]: File: C:\Windows\pyw.exe;	To be installed;	Won't patch;	No existing file
MSI (s) (34:04) [14:27:19:606]: Source for file 'pyw.exe' is compressed
InstallFiles: File: pyw.exe,  Directory: C:\Windows\,  Size: 102912
"""