How A Virus Infect A Cell?

I have been thinking...why flu only attack our upper part respiratory tract? why HIV only attack our T cells?

ok here's what i think about after reading and searching the net...

Virus like can recognize the cell they want to attack only... and i think that the Glycoproteins play a huge role as glycoproteins are membrane proteins which play important roles in cell recognition.

this lead me to think that it is almost same as the "lock and key" hypothesis as i learn in the enzymes chapter. Virus is act the key and and the host cell is act as a lock.
Key and only fit in a certain or specific lock that is suitable for the key. So thats why HIV only attack the T-cells but not the other cell such as erythrocytes, nerve cells, muscles cells etc...

Quote from websites:

"The flu virus then attaches to a receptor, CD54 (Cluster of Differentiation 54), which is located on the surface of cell of the lining of the nasopharynx. The receptor fits into a docking port on the surface of the virus. Large amounts of virus receptor are present on cells of the adenoid. After attachment to the receptor, virus is taken into the cell, where it starts an infection. "

and

"CD4(Cluster of Differentiation 4) is a primary receptor used by HIV-1 to gain entry into host T cells.

HIV-1 attaches to CD4 with a protein in its viral envelope known as gp120(a glycoproteins that exposed on the surface of the HIV envelope ). The binding to CD4 creates a shift in the conformation of gp120 allowing HIV-1 to bind to surface receptors on the host cell. HIV inserts a fusion of peptide into the host cell that allows the outer membrane of the virus to fuse with the plasma membrane then evades the cell"

so i made a conclusion:
A virus only infect a certain cell base on the glycoprotein at the surface of the cells.

please correct me if i say wrong anything above thanks.