I can only shed light on a tiny sliver of the answer to this question. One of the reasons you don't see modern buildings near Vatican City in Rome is that tall buildings are actually forbidden by treaty--the Lateran Accords. This treaty was signed in 1929 and regularized the relationship between the new nation of Vatican City and the Italian state (solving the "Roman Question" that had lingered since 1870), and the treaty is still in force today with very minor changes. The relevant section is Article 7:

The Italian Government undertakes to prohibit the construction within the territory surrounding the Vatican City, of any new buildings which might overlook the latter, and shall for a like purpose provide for the partial demolition of similar buildings already standing near the Porta Cavalleggeri and along the Via Aurelia and the Viale Vaticano.

In accordance with the provisions of International Law, it shall be forbidden for aircraft of any kind whatsoever to fly over Vatican territory.

On the Piazza Rusticucci, and in the areas adjoining the Colonnade, over which the extra-territoriality referred to in Article 15 hereof does not extend, all structural alterations or street construction shall only be effected by mutual assent.

As you can see it is actually forbidden to build any new buildings that would overlook the Vatican. Hence, there are no 50-story high rise office buildings or apartments in the area.

Paris went through a number of urban transformations, starting with the Pont Neuf, the Places Royale and des Vosges, and the remaking of the Ile St. Louis in the 16th and 17th centuries. This also includes widening of streets into boulevards, including the tearing down of the city walls to create a circular walking boulevard around the old city, only to have it rebuilt 70-80 years later in order to better collect taxes from merchants bringing goods into the city.

Baron Haussman in the 19th century performed similar reinvention of Paris, removing, widening, and straightening of streets into easily navigated avenues, to make the views more alluring and aesthetically pleasing, as well as easily pass from one side of Paris to the other. This also includes today's parks around Paris and the current structure/format of the Champs d' Elysses and other avenues, giving Paris that specific architecture (cream buildings, 4-5 stories tall) that it is famous for.

In the 20th century, Paris passed a regulation limiting buildings within city limits to be no more than 121 feet tall. This was done after the construction of the Tour Montparnasse was completed (at roughly 700 feet tall). Many residents felt that the modern skyscraper took away from the beauty of Paris. (Having been to both Manhattan and Paris, I have to agree with them!) This has recently changed (in 2010 or 2011 iirc) allowing specific areas to build up to roughly 200 meters tall in order to keep more Parisians IN Paris, rather than move to the suburbs, and to decrease congestion moving in and out of the city.

Sources: How Paris became Paris - Joan DeJean, Parisians - Graham Robb, Paris Reborn - Stephane Kirkland