Now, so far as I have been able to tell, there is nothing in those first paragraphs of Universae Ecclesiae that is not already in Summorum Pontificum. In fact, one can take most of those first paragraphs, turn to Summorum Pontificum, and look to find where they are in "the original". It is really a summary of the provisions, or the underlying principles of the provisions, of Summorum Pontificum.
So, for example, this from Universae Ecclesiae
could, if one were publishing a concordance of such things, be placed alongside this from Summorum Pontificum:6. The Roman Missal promulgated by Pope Paul VI and the last edition prepared under Pope John XXIII, are two forms of the Roman Liturgy, defined respectively as ordinaria and extraordinaria: they are two usages of the one Roman Rite, one alongside the other. Both are the expression of the same lex orandi of the Church. On account of its venerable and ancient use, the forma extraordinaria is to be maintained with appropriate honor.
If we also recall that, in his letter accompanying Summorum Pontificum, Pope Benedict wrote:Art 1. The Roman Missal promulgated by Paul VI is the ordinary expression of the "Lex orandi" (Law of prayer) of the Catholic Church of the Latin rite. Nonetheless, the Roman Missal promulgated by St. Pius V and reissued by Blessed John XXIII is to be considered as an extraordinary expression of that same "Lex orandi," and must be given due honor for its venerable and ancient usage. These two expressions of the Church's "Lex orandi" will in no any way lead to a division in the Church's "Lex credendi" (Law of belief). They are, in fact two usages of the one Roman rite. It is, therefore, permissible to celebrate the Sacrifice of the Mass following the typical edition of the Roman Missal promulgated by Blessed John XXIII in 1962 and never abrogated, as an extraordinary form of the liturgy of the Church.
..., it is clearly seen that the new Missal will certainly remain the ordinary Form of the Roman Rite, not only on account of the juridical norms, but also because of the actual situation of the communities of the faithful....The celebration of the Mass according to the Missal of Paul VI will be able to demonstrate, more powerfully than has been the case hitherto, the sacrality which attracts many people to the former usage. The most sure guarantee that the Missal of Paul VI can unite parish communities and be loved by them consists in its being celebrated with great reverence in harmony with the liturgical directives.we can begin to see what I might call an element of mischief. If one reads the Instruction without reading the Motu Proprio (and, after all, the Instruction is about the implementation of the Motu Proprio, so one should really read the Motu Proprio with the Instruction) one can gain a rather different sense of the intended "balance" between the two forms of the Roman Rite. One could take away from the Instruction a sense of "equivalence" between the ordinary and extraordinary forms - prompted by the absence of the assertion of the ordinary form as being the ordinary form in a real sense as well as a juridical sense and the insertion (compared to Summorum Pontificum) of the phrase "one alongside the other". I do not think that such an "equivalence" is intended or expressed in the provisions of Summorum Pontificum.
As someone who does not have an attachment to the extraordinary form, and who sees the value to the vast majority of Roman Catholics of Summorum Pontificum and its more generous provision for celebration of the extraordinary form in the mutual enrichment of the ordinary form resulting from that more ready celebration of the extraordinary form, I do not find this element of mischief helpful. We have a stake in the project of Summorum Pontificum, just as much as do those attached to the extraordinary form, though that stake is of a different nature. [And before anyone complains about my use of the word mischief, do read it within the genre in which it is written and remember that, if you are complaining about my use of the word here, it's quite likely that you wouldn't complain about it if I were referring instead to the work of the post-conciliar Consilium or of ICEL in its pre-new-translation incarnation.]
Oh dear, I am off message again ... More to follow.
UPDATE: The effect of this mischief is exemplified in this extract from Fr Zuhlsdorf, where the influence of the insertion "one alongside the other" and the omission of the recognition of the Missal of Paul VI as the ordinary form in reality as well as juridical nature is quite apparent. What it says is both perfectly correct and perfectly incorrect (though both in different senses).
The Instruction could have said that the Extraordinary Form is not to be used as often as the Ordinary Form. It doesn’t. It says that the Ordinary and Extraordinary Forms are “one alongside the other” and that the Extraordinary Form is to be maintained with “appropriate honor”.